More blue water - why is the Nil Diya Pokuna blue?

On my last visit to Sri Lanka, I was keen on exploring some lesser-known attractions and decided to visit Nil Diya Pokuna (නිල් දිය පොකුණ) located close to Ella in the Uva Province. I was impressed and fascinated by the massive underground cave complex and the blue water pond at the end of the 850m hike through the cave. This was the second time I saw clear blue water in Sri Lanka, the first being in a limestone quarry.  

The usual reason for ponded water to appear bright blue or turquoise in colour is the fine particulates that selectively scatter light through water (the same reason why the sky is blue). In the case of the limestone quarry the fine particulates are minute calcite crystals and in the case of glacial lakes they are finely ground rock particles known as glacial flour. 

Nil Diya Pokuna has a very interesting geology, with several different rock types present around and within the caves, and I wanted to understand what gives the water its blue colour. Caves of this scale are usually formed by the action of weathering and erosion of sedimentary rocks such as limestone. However, this region of Sri Lanka consists of primary of metamorphic rocks. This blog post by Dr Jayasingha describes the geological origins of the cave complex containing Nil Diya Pokuna. According to it, the caves have been formed by the initial dissolution of Marble, which leads to weakening of rock joints and bedding planes and subsequent collapses of the other rock masses creating the large underground caverns. 

Marble is formed by the metamorphosis of limestone, and its dissolution would lead to the release of calcite crystals. There are stalactites formed at several places within the cave, as seen in the photos below, that confirm the occurrence of marble or limestone dissolution. Therefore, it is reasonable to conclude that the reason for the blue coloured water in Nil Diya Pokuna is the calcite crystals that are accumulated in the water as it flows through the joints and fissures in rock containing marble or limestone before making its way into the pond. Below are some photos from my visit:

Stalactites in the cave indicating marble or limestone dissolution
 

Evidence of weathering and staining in the rock

Visible bedding planes and smooth joint surface of a possible collapse leading to cave formation

Blue water and more stalactites

High water levels were blocking off some more expansive areas of the cave

The water was a little murky due to recent rains

Another web app to estimate the soil water retention curve

I created another simple web application to estimate the soil water retention curve from basic particle size distribution data. I used the equations developed by Zapata et al. (2000). The water retention curve can be exported as before and the previous app can be used to estimate hydraulic conductivity and oxygen diffusion coefficient of the soil after fitting to the vanGenuchten model.

Link : https://rukshan-azoor-psd.anvil.app/

I have also embedded the app below:  

Connecting Adam's Bridge

Adam's Bridge, the collection of limestone shoals between the Mannar Island of Sri Lanka, and the Pamban Island of South India has sparked both the imagination and inventive thinking of many. The closest distance between the two countries-between Dhanushkodi, and Talaimannar is about 30 km, and a bridge connecting the two countries has been a long argued prospect. Such a bridge will be beneficial to both countries in terms of economics and trade. The engineering and environmental challenges of such a construction are overwhelming and a unique Geo-chemical engineering method might hold the answer to this problem.

The Jaffna Peninsula and the surrounding area consists of a Miocene limestone basement and the sea in the area of the Palk Strait is very shallow. This makes it possible to easily construct a permanent causeway between the two countries by connecting the limestone shoals of the Adam's Bridge. Although a simple construction, a permanent separating structure will disrupt the sediment movement through that channel and can be detrimental to fisheries as well. The complete disconnection of the water circulation through the gap can pose significant environmental problems. Building a bridge across the entire span is a possibility that is too costly. Therefore the ideal solution would be to construct a combined, landmass-bridge structure.

http://www.geo.shimane-u.ac.jp/spfs/g_students/mext/08sansfica/Sansfica08_2L.jpg

 To support the construction of a bridge, the existing landmasses or shoals should be elevated. Bridges can be constructed on these elevated landmasses while leaving gaps for the flow of water. Some of these gaps can be dredged deeper to allow for the same volume of water to flow. This could also serve the purpose of a navigable channel for ships as proposed by the Sethusamudram Project. Another prospect is for electricity generation by means of hydro-turbines installed at gaps where the flow of water will be heightened.

It is in elevating these landmasses that the unique geo-chemical engineering method comes into play. Research conducted by Prof. R.D. Schuiling indicates that these landmasses can be elevated in a cost effective manner by injecting Sulphuric acid into the limestone basement. The principle here is that, Sulphuric acid will react with the limestone to produce Gypsum, which has a higher molar volume. Thus, the rock will expand, and this expansion will be accommodated by surface uplift. (R.D.Schuiling, Current Science Vol 86).

This process involves drilling bore holes along the trend of the Adam's bridge and injecting Sulphuric Acid at modest pressures insufficient for hydro-fracturing. The well jointed Miocene limestone is expected to facilitate the migration of the acid through the basement. The acid will be injected to bottom layers of the limestone leaving the top layers unaffected thus avoiding contact with the biosphere and and associated environmental problems.

Prof. Schuiling points out that if industrial waste Sulphuric acid is used for the process it would be an economically viable technology while also solving the disposal problem of such acids. He further addresses possible environmental effects. Since the expansion of the rock takes place at the bottom layers and is separated by a layer of un-reacted limestone, there won't be direct consequence from the reaction. As for the concerns with heavy metals if waste acids are used, it has been experimentally proven that such heavy metals are immobilized during the reaction.

While a social and political consensus regarding the construction of the Adam's Bridge has not yet been reached, and no comprehensive EIA has been conducted in this regard, if these happen in the near future and if the two countries go ahead with the project, this Geo-chemical engineering technology will be a compelling prospect.

Beach Nourishment in Sri Lanka

Beach Erosion is a problem faced by many countries and erosion mitigation has been traditionally done using hard engineering solutions such a seawalls, revetments, groins and breakwaters. However, research in this field has identified that such engineered structures are not suitable as long term solutions for erosion as they interfere with the dynamic coastal processes. It has also been suggested that soft engineering solutions which work along with these coastal processes are the best approach in solving the problem of beach erosion. Beach nourishment is currently the most popular soft engineering solution and is increasingly being used to protect beaches all around the world. Sri Lanka has also joined this trend and completed its first beach nourishment program along a 1.8km stretch in the the Uswetakeiyawa Palliyawatta area in early 2012.

The project involved a large capital investment and a total of volume of 300,000 cubic meters had been used in the nourishment process. The sand used to nourish the beach was offshore sand dredged using a vessel anchored far away from the coastal zone. This is important because, using sand in the coastal zone itself would have been ineffective. The dredged sand had been pumped via pipeline and released as a slurry onshore and the beach reconstructed using earth moving equipment. Several offshore breakwaters had also been constructed with the intention of retaining the nourishing sand. While the project seemed to be an initial success with positive results shown in surveys carried out immediately before and after the project, over a period of time it is evident that the nourishment has not changed the rate of erosion. At present, the beach has once again severely eroded and continues to erode despite the breakwaters.

Severe erosion of the nourished sand

The success of a beach nourishment program depends on many factors. Coastal processes such as waves, near-shore currents, tides and even wind affect the nourishment process. Parameters such as beach profile and gradient and grain size of sand also matters in this regard. For this reason, a beach nourishment effort is site specific and all these site specific data needs to be considered when planning a nourishment program. In addition, it also vital to continuously monitor the performance of the beach after nourishment and to take necessary remedial action to maintain the project.

While most of the above information had been gathered prior to the nourishment project at Uswetakaiyyawa, the effort has fallen short in post project monitoring. The construction of breakwaters to retain the sand being a tried and tested method, has failed to perform properly possibly due to incorrect layout and dimensions of the breakwaters. Our final year research project aims to assess the performance of this nourishment effort and to provide a solution to the problems faced in this project.

To do this, beach profile measurements are taken using a dumpy level and total station along transects perpendicular to the nourished coastal strip. This process is done during several visits to the area covering the main seasonal cycle of the country. This data is used to model the beach profile and to analyse the sand volume changes with respect to time. A particle size analysis is performed on samples collected at each transect and will be used to determine the direction and severity of the sand transport. In addition to this, a temporal analysis of satellite images is also expected to be incorporated in the research in order to further enhance the field data. Using these findings, our research team expects to propose a suitable solution to minimize the rate of erosion and provide a methodology to effectively monitor beach nourishment programs in Sri Lanka. This would be of immense use in future nourishment projects in the country.

Mining for Petroleum

Although Mining Engineering and Petroleum Engineering are two different fields of study, the two fields cross paths when it comes to the Oil Sands Industry. Oil Sands refers to the deposits of petroleum in the form of heavy bitumen being present in a mixture of sand or loosely consolidated sandstone. Because this heavy oil is too thick to flow and because it is thoroughly mixed with sand, the conventional methods of extraction of petroleum by drilling cannot be applied here. For this reason and also if the oil sand deposit lies relatively close to the surface, open pit mining is used to extract the oil sands. Once mined, the sands are processed to produce synthetic oil.

The mining for oil sands begins like in most mines by the overburden removal process. Common machinery such as excavators, bucket scrapers, and bulldozers are used to remove the overburden and the overburden is hauled by trucks and piled separately for refilling purposes. Once the overburden is removed and the oil sand layer exposed, the mining process begins. Since the oil sand deposits are unconsolidated, they can be easily be extracted by shovels or excavators. For this reason and for obvious safety reasons blasting is not performed. In addition to these machines, draglines and sometimes continuous excavators such as bucketwheel excavators are also used for mining the oil sands. The mined sand is hauled to a plant where the petroleum is extracted and refined by a variety of processes including crushing, froth flotation and distillation.

Although previously termed as an unconventional source of petroleum, the depletion of "conventional oil" and the associated rise in oil price has resulted in a shift of attention towards the oil sands industry. The largest oil sands deposits are located in Canada and Venezuela and the total volume of oil contained in the sands exceeds the conventional oil reserves of the world.  Oil sands have been commercially extracted in the Athabasca region in Canada since the 1930s and since have developed along with the advances in extraction technology. The following graph shows the value of sales  of oil sands and conventional crude oil in Canada and it can be seen that the oil sands sales have shown a significant rise during recent years.

value of sales of crude oil and oil sands (data taken from : http://www.capp.ca/library/statistics/Pages/default.aspx)

New methods have been developed to extract oil sands deposits that are too deep to extract using surface mining. These methods involve the reduction of the viscosity of the bitumen and the separation from the sand and enables the oil to be pumped to the surface. These methods are termed "In-situ methods". Cyclic Steam Stimulation (CSS), Steam Assisted Gravity Drainage (SAGD) and Toe to Heal Air Injection (THAI) are some of these methods. With advances in in-situ methods like these, the the recovery percentages of oil sands deposits have increased and now it can be considered as a viable alternative to conventional oil.

Limestone Mining in Pictures

In this post I have attempted to summarize the limestone mining process in pictorial form (and a video). Short descriptions have been included where necessary.

Overburden Removal

once the overburden is removed, the beds are cleaned and are prepared for drilling

Drilling

drilling is performed according to a pre determined pattern to accomodate explosives for blasting

Blasting

Rock Blasting is performed to fragment and loosen the consolidated limestone.

Loading and Hauling

Dispatching 

Tyre Maintenance of Mine Machinery

The performance of machinery and their availability plays a major role in the productivity and output of a mine. For this reason, every aspect of the machines should be properly maintained. The tyres of these machines are what keeps the machine in contact with the ground and bears the weight of the machine. While tyres for mining machinery are designed to withstand a beating, incorrect maintenance can reduce lifetime of the tyres, or ultimately lead to catastrophic accidents. Therefore, the proper maintenance of the tyres is as important as the maintenance of any other component of the machine.

Handling large tyres of the gigantic mine machinery is not an easy task. Even a simple task such as changing the tyre is difficult and results in a considerable amount of downtime. Therefore the best strategy in this case is preventive maintenance. This means checking tyre inflation daily, ensuring that valve caps are on, checking tread depth and removing stones and other debris lodged between the treads.

changing tyres is a difficult task

When it comes to daily maintenance, the first thing that comes to mind is the inflation pressure. Both over-inflation and under-inflation are detrimental to the tyre, and therefore, it must be ensured that the inflation pressure lies within the accepted limits. It should be noted that when running the machine the tyre pressure increases by about 10-20 percent. Therefore, this must be taken in to account when setting inflation pressure bounds. Tyres kept in good condition with the proper inflation will last longer and perform better.

External conditions of the mine also affect the tires. The road condition for example is what determines how fast the tyres will wear out. While it is not practical to maintain spotless roads, roads should be kept clear of scattered rocks and sharp pits as driving over these can cause a crack in the rubber, and subsequent running will cause it to propagate and destroy the tyre. Therefore clearing fallen debris off the roads and maintaining the road surface is also a part of tire maintenance. Wet rubber cuts better. therefore it is best to avoid wet road conditions. While most haul roads in mines are watered regularly to minimize dust, it must be ensured that the roads don't get too wet.

Bad road conditions can cause cracks to develop

The handling of the machines and their usage are two other areas that need to be considered. Driving too fast, especially in the case of dump trucks can cause several types of tire damage. In the case of heavy machinery used in mines, a combined parameter combining both speed and weight is assigned to tyres. This parameter is called the TKPH rating (Ton Kilometer per Hour). The TKPH rating should be considered when selecting and using tyres. When loading dump trucks, they should be loaded symmetrically so that the load is distributed over tyres equally. asymmetric loading can cause uneven wear and later result in more severe damages. It should also be noted that shear forces generated when steering the trucks while stationary at the loading points could cause ruptures in the tyres.

When dealing with damaged tyres, it is always best to attend to it them at the start of the problem. Neglecting small faults like cracks and running with them can cause these small faults to quickly propagate and result in serious and irreversible damage. When a crack appears it can be removed altogether by cutting around it. This however has to be done with proper equipment and knowledge of the tyre. When replacing tyres, it is always best to replace it with a tyre of similar amount of wear.

In summary, daily maintenance goes a long way in increasing the lifetime of the tyre. Inflation pressure must always be within the specified limits. The road surfaces, loading and dumping points should be free of fallen debris and excessive water, because wet rubber gets cut better. payload weight and hauling speed must be controlled. The TKPH rating assigned to the tyre must be adhered to. Proper handling of the machinery such as symmetric loading, avoiding steering while stationary and avoiding excessive tyre spinning will reduce the likelihood of damages. when repairing, the first stages of the problem is always easy to cure.

Creating a 3D Terrain Model using Surfer

A three dimensional model of a particular land feature can be very useful for visualization. A 3D model which can be manipulated in a digital environment is even more useful, especially if volume calculations need to be performed. A good software package for this purpose is, "Surfer". It has a relatively simple user interface and is easy to learn.

Essentially what Surfer requires to create a 3D surface model is a set of spot heights along with their northing and easting coordinates. The data can be imported into Surfer by many ways, of which using a MS Excel file or an ASCII text file are simplest. The software will interpolate the data points and create a surface. The algorithm used for interpolation can be changed according to the requirement.

Obtaining spot heights of the area can be done by performing a level survey. If high accuracy is not required, a quick and easy method of obtaining spot heights is to overlay a grid with known coordinates over a topo sheet with contours. Using the contours, the heights of the vertices of the grid can be determined. Since the northing and easting of the grid are also known, it can be fed into Surfer via MS Excel Another method of creating a 3D model using Surfer is to directly import a DEM (Digital Elevation Model) into the software. DEMs can be downloaded from the USGS website.

A simple volume calculation based on spot heights obtained by the gridding method is illustrated below.

First, the grid was drawn over the contour map in the AutoCAD environment. In this example, the contour interval is 2 m, and the grid spacing has been selected as 3 m.  

The spot heights were found by using the contours closest to the vertices of the grid and the data was entered as x, y and z coordinates into an MS Excel sheet.

Using Surfer, the excel sheet was input and a grid file was created. (Grid>Data). The gridding method used for this example is "Kriging". Other methods can be used depending on the requirement.

A 3D surface was created using the grid file previously created.

This 3D surface can be used for volume calculations as well. For example, Consider that the trough indicated in the above terrain model needs to be filled with water, up to the 8m contour level and it is required to calculate the volume of water required.

This means we need to calculate the volume between the modeled surface and the plane z=8. To do this, the volume calculation dialog box was opened (grid>volume..) and the upper surface was given as z=8 and for the lower surface, the grid file was selected. The calculated positive volume indicates the volume of water required to fill the trough. In this example the calculated volume is, 696.73 cubic meters. 

Optimization of production of a Mine

The main objective of a mine is to extract a mineral deposit in an economical manner and to maintain a continuous output. In order to do this, the operations performed in and out of the mine must complement each other. While intensive planing and monitoring of all unit activities is required to achieve this, the following steps will help to optimize production and reduce cost thereby increasing efficiency.

Calculate and plan production targets and compare with actual production.

In order to determine whether a mine is operating efficiently, first targets should be established. To do this, drilling and blasting cycles and hauling capabilities can be factored in initial calculations. To set more specific production targets, modelling software can be used. The important thing is to compare the actual data with these targets and to take corrective action when the production does not meet the target.

Maintain a buffer stock of material

While in normal conditions, production can be carried out without interruption, due to various reasons the rate of production can decrease or in worst cases, halt altogether. Interruptions due to bad whether in open pit mines is a good example for this. To cope up with these delays it is essential to have a stockpile of material ready to be dispatched. This stockpile will act as a buffer until production resumes and the mine will produce the expected output throughout.

Proactive maintenance of machinery

Several approaches can be taken in the case of maintenance of mine machinery. in order to minimize losses due to downtime and faulty operation it is best to employ a preventive or proactive maintenance strategy. When doing maintenance work, it is vital to get operator feedback as it will help to diagnose problems better. Another very important fact to be considered when acquiring a new fleet of machines to a mine is to obtain all the machines of one particular brand. This ensures inter machine compatibility. It also saves time and resources in ordering, acquiring and using of spare parts.

Streamline work and physical movement

A mine is a place of continuous movement. To increase efficiency, these movements must be streamlined and effective. This means that access paths and haulage ways must be as short as possible with sufficient room for maneuvering. The mine layout itself must be orderly and separate operations should not disturb each other(except in unavoidable circumstances such as blasting). These reduce cycle times of the mine and increase production.

Safety

This is a factor overlooked in most mines. However safety plays a major role in the overall efficiency of the mine. A mine with a lot of accidents suffers a lot of downtime and it will reduce production. Proper safety procedures will enable continuous operation and will also enhance working conditions, both of which will ultimately result in an increase in efficiency.

Global Tidal Variations Explained

Tides are periodic variations of the ocean surface caused by the gravitational attraction of the moon and the sun. On a fundamental level, tides can also be considered as waves. Since these tidal waves have extremely long wavelengths, they are essentially shallow water waves(Shallow water waves are waves which travel over depths lower than 1/20th their wavelength). This means that the speed of the tidal wave is proportional to the depth. The depth of the ocean basin, the time of year and month, latitude and earth's rotation affect the type and magnitude of tides. While the exact relationship between all these variables can be somewhat complex, certain scientific theories and models help simplify and explain the behavior of tides.

Depending on the occurrence of high and low tides, tidal patterns are classified into three types. These are,
1. Diurnal tides
2. Semi-diurnal tides
3. Mixed Tides.
If the tidal wave shows 1 crest and 1 trough within a period of 1 lunar day(24hrs and 50mts), then it is called a diurnal tide. If it shows two crests and two troughs or vice versa in one lunar day, it is called a semi-diurnal tide. Mixed tides are a mixture of these two, often with significantly different amplitudes.

While tidal variations can be attributed to the gravitational attraction of both the sun and moon, the effect of the moon is significantly larger. "The Equilibrium theory of tides" attempts to explain these variations with the following assumptions.
-the ocean is indefinitely deep
-no land masses are present
-no inertial forces
With these assumptions, the key tide generating forces are, gravitation and centripetal force. These two forces act differently on different locations on the earth. While the gravitational force directs to the center of the moon, the centripetal forces at different locations are parallel to each other. This is because, centripetal force is the force that keeps an object in circular orbit, and the different locations have their own circular orbits parallel to each other.

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

The gravitational attraction provides the required centripetal force to keep the earth in orbit. However, the gravitational attraction and the required centripetal force are unequal at different locations on the earth. These two are equal only at the center of the earth. The difference between these two forces creates a resultant force which acts as shown in the diagram. It is this resultant force that is responsible for the generation of tides. This is also why, tidal bulges appear on both sides of the planet, because the resultant forces at the two sides of the earth are oppositely oriented. 

The orbital plane of the moon is inclined by approximately 28.5 degrees to the earth's axis of rotation. This causes the tidal bulges also to orient as shown below. The earth rotates through these tidal bulges. This explains the occurrence of diurnal and semi-diurnal tidal patterns explained above. By inspecting the diagram below it can be seen that high latitude locations receive diurnal tides, equatorial regions receive semi-diurnal tides and mid latitude locations receive mixed tides. 

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

This shows how the equilibrium theory explains the occurrence of the diurnal and semi-diurnal tides. This means that, tidal patterns on earth should be related to latitude. According to the above diagram it is also seen that tidal heights should also vary with latitude, with the highest tidal heights in mid latitude regions. However, the following tide map of the world shows that no such connection between tidal characteristics and latitude can be observed. This is where the equilibrium theory of tides fails.

-world tidal patterns- Source : Invitation to oceanography / Paul R. Pinet. — 5th ed.

The equilibrium theory of tides does not take into account the depth variations of the ocean basins. It also neglects the effect of the earth's rotation. To overcome these issues, another theory, "The Dynamic Theory of Tides" was proposed. Proposed in the 18th century by Pierre Simon Laplace, it attempts to explain tidal variations with the Coriolis Force.

To illustrate this theory, consider a large rectangular ocean basin in the northern hemisphere. when the water level rises in the upper portion of the basin due to the tidal action, the Coriolis force deflects the mass of travelling water towards the right. this causes the water to build up in the upper right corner of the basin. The resulting pressure gradient causes the water to flow downwards, but is again deflected to the right by the Coriolis force. This cycle continues, and it results in a counterclockwise oscillation of the water mass. The nodal point where the water does not oscillate is known as an "Amphidromic Point."

Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

If the ocean basin is situated in the southern hemisphere, the Coriolis force will deflect the water towards the left side, and the resulting oscillation would be clockwise. While ocean basins found on earth are not ideal basins like the above explained, several Amphidromic Points can be identified in the earth's oceans through tidal action. This amphidromic system of tides better explains the tidal variations depicted in the above tidal map. Since the amphidromic system is an oscillatory system, tides can undergo resonance. If the natural period of the ocean basin equals the period of the tides, tidal resonance will occur creating a massive tidal wave. An example of this is the Bay of Fundy where tidal ranges of over 17metres have been observed.

Global Amphidromic Points - Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

The depth of ocean basins also affect tidal heights. As explained above, tides being shallow water waves, have speeds that are proportional to depth. This means that a lower depth would cause the tidal wave to slow down, and due to the conservation of energy, the amplitude of the wave would increase, thus creating a higher tide. Taking all these factors into consideration, tides can be accurately modeled and predicted.

This understanding of tidal action opens up means of using it as an energy source. In places where a high tide variation is present, tidal energy can be tapped into by building dams to trap the incoming tidal flood current, and then channeling them through turbines like in a hydro-power plant. Power plants of this type are already in operation around the world, an exmaple is the La Rance tidal power plant at St. Malo, France. Tidal power plants do not pose a significant threat to the environment and are therefore are a good alternate source of renewable energy.

Geochemical Environment

The Geochemical Environment is defined by the surrounding conditions of pressure, temperature, and abundance of chemical components. The geochemical environment influences the ore body formation and dispersion. Therefore a clear understanding of the geochemical environment is essential in mineral exploration.

The geochemical environment can be classified into two types based on the conditions of temperature, pressure and chemistry. They are,
1. Endogenic Environment.
2. Exogenic Environment.

The Endogenic Environment is the deep-seated environment in which forces driven by earth's internal heat predominate. Since rock formation often takes place in this environment, it is also called the "Primary Environment". Metamorphic conditions, magmatic, igneous conditions, activities in the vicinity of plate boundaries and sometimes deep seated sedimentary conditions are geological activities that are prominent in the endogenic environment. The endogenic environment can be characterized by,
- high temperature
- high pressure
- lack of free oxygen
- lack of free water and CO2
- restricted movement of fluids

The Exogenic Environment is the surficial environment in which forces are mainly driven by solar energy. It is also termed the "Secondary Environment". Geological activities present in the exogenic environment are, weathering, erosion, transportation and sedimentation. The exogenic environment can be characterized by,
- low temperature
- low pressure
- abundant free oxygen
- abundant water and CO2
- free movement of solutions

These two environments are connected to each other and material gets transported from one to another creating a closed system. Driven by the natural forces described above this dynamic system can be simplified and depicted in the diagram below. A good understanding of this cycle can help decision making in the mineral exploration process.

the geochemical cycle(Image from "Geochemistry in Mineral Exploration" by Rose et al)

Basics of Photogeology

The interpretation of Aerial Photographs for geological purposes is termed Photogeology. This a form of Remote Sensing. The primary objective of Photogeology is, to identify geological structures and rock types of an area and to prepare a geological map of the area. Photogeology is usually employed before field geological work in order to get a general idea of the geological features of the area. The observations and inferences obtained from Photogeology are then confirmed by using field data.

The analysis of aerial photographs in photogeology is done using the same elements of interpretation. "Tone" is used in the identification of rock type. Generally lighter tones indicate rock types like Quartzite. Tone is also used in the identification of the density of vegetation which in turn provides clues about the underlying rock. Usually dense vegetation can be seen in area where the rock Khondalite is present and in areas where Quartzite is abundant, very little or no vegetation is present.

By using a stereoscope to view the three dimensional topography of the area structural features such as ridges, valleys and slopes can be identified. Due to differences in hardness and the extent of weathering, certain rock types show characteristic structural features. For example, Marble and Hornblendebiotite Gniess are found at the bottom of valleys because they are highly prone to weathering. Rocks that are much harder and are resistant to weathering like Quartzite, Granite and Granitic Gneiss usually form ridges.

geological features in an aerial photograph

When viewing outcrops from above, for example in a ridge like structure, by looking at the texture on either side of the ridge, the direction of dip and strike can be inferred. Since the side where multiple layers of rock are exposed undergoes differential weathering that side become ragged and rough. This side is termed the escarpment face. The side on which a single layer of rock is exposed undergoes uniform weathering and therefore is relatively smooth. This side is the Dip slope. Therefore, generally the side of a ridge that has a relatively smooth texture indicates the direction of dip.

cross section of a ridge

The drainage pattern and shapes of marshes lakes etc also provide clues about the geological structure of the area. A drainage pattern like shown in the first diagram indicates a homogeneous and relatively flat rock while a pattern like in the second diagram indicates a highly jointed rock. In addition to this, the displacement of any feature along a line indicates a rock fault.

Once all possible features are identified form the aerial photograph, a geological map of the area is plotted. This map is referred and then the data is confirmed by using field data.

 

Stereoscopic Analysis of Aerial Photographs

Aerial Photographs were the primary source of visual information used in Remote Sensing before satellite imagery became widely available. Stereoscopic analysis of aerial photographs were widely used for reconnaissance purposes during the world war. Apart from this, interpretation of aerial photographs have proven to be useful in various field of study such  as geology, surveying, mine planning and development and even environmental studies.

aerial photographs, stereoscopes and a map.

A typical aerial photograph usually contains, information such as the flight line, time of capture, altitude and the photo number. The flight line and photo number becomes useful when locating the photographed area on a map. The scale of the photo is also an important detail. The scale can be obtained by dividing focal length of the camera by the vertical distance from the imaged ground, to the camera. Aerial photographs can be panchromatic(black and white), colour, or in any other band of the electromagnetic spectrum. These details should be selected depending on the scope and objective of the image analysis.

In the process of interpreting aerial images, several interpretative elements are used in order to make the task of identifying and interpreting objects in aerial photographs easier and systematic. These elements of interpretation are,

Shape - The general outline or form of the object. regular and irregular shapes can help identify natural and artificial object.

Tone/Colour - It refers to the relative brightness or colour of an image. While in colour images, objects can be identified by it associated natural colour alone, in panchromatic images identification is slightly more difficult with varying shades of grey.

Size - Refers to the physical extent or the dimensions of the object. It is often useful to assess sizes of objects relative to each other.

Texture - Refers to the frequency of tonal change in an area of an image. can be described as smooth, coarse etc. For example; water appears smooth while a forest canopy shows a rough texture.

Shadow - shadows provide valuable information about the height of an object while also being a tool of identification of certain features in monotonous areas. For example, shadows can help identify lamp posts, water towers which would otherwise be misinterpreted because of its plan view. Shadows can also help identify sand dunes in a desert.

Pattern - Pattern is the spacial arrangement of objects on the landscape. can be describes as regular, ordered, irregular symmetric etc. Can help distinguish agriculture from natural vegetation.

Association - refers to the fact that certain features and activities are always related to the presence of certain other features and activities. This association of one object to another helps the process of identification and also can provide additional information of the area under analysis. For example, a populated area indicates the presence of roads and other infrastructure and an area with fuel tanks, chimneys etc could imply that the area under observation is a power station.

Identifying most of these features using two dimensional images is a very difficult task and can lead to confusion.The identification of the objects in a photograph using the above elements becomes very easy in three dimensions. In order to view aerial images in 3D, a modified version of the simple lens stereoscope is used. 

stereoscope

 This stereoscope which is used in aerial photograph interpretation, consists of a set of mirrors that reflect the aerial photographs laid on the table into the two eyepieces. The photographs used here are overlapping each other and by viewing a two slightly displaced images through each eye, the 3D effect is created.

While proving clues about an objects height, a three dimensional view of an area can also avoid confusion created by similar textures and tones. For example, mountainous terrain without significant vegetation can appear as a flat terrain if not for the stereoscopic view. It also helps to follow the flow path of streams and rivers where subtle tone changes or other disturbances have hindered a direct view.

Geochemical Exploration

Geochemical Exploration is defined as, "The systematic measurement of one or more chemical properties of naturally occurring materials to identify abnormal chemical patterns or geochemical anomalies related to mineralization". In simple words it means, the identification of mineral deposits by the use of chemical methods. Although geochemical exploration alone is insufficient to detect and pinpoint ore reserves, it is used in conjunction with geologic and geophysical exploration methods. However when the effectiveness of geologic or geophysical methods become limited due to certain reasons, geochemical prospecting becomes a useful tool to confirm the presence of mineral deposits.

The term "Mineral deposit" is defined as an abnormal concentration of a naturally occurring material(Note that "economic viablity of extraction" is not included in the definition anymore). Since an abnormal concentration of any naturally occurring material is bound to leave behind traces, the objective of geochemical exploration is to identify these clues left by the mineral deposit and to use them to locate it.

Geochemical exploration usually includes the measurement of concentrations of group elements, trace elements, and single elements in,
- Soil, rock, Sediment
- Water, (sea/river)
- Plant material
- Glacial Debris
to determine geochemical anomalies that might indicate a mineralization. Before carrying out the investigation it is essential to have an idea about the behaviour and characteristics of the chemicals involved, the exploration methods to be used and the analytical techniques to be used. Once these factors are considered, proper planning and preparation will help optimize the exploration.

Depending upon the ways of sampling and analysis several methods of Geochemical exploration or surveys can be defined.

Stream sediment surveys - this is of two types, stream sediment panned concentrate surveys and stream sediment surveys. this method is used when heavy minerals and chemicals that bond with clay are involved.

Soil Geochemical surveys - used when looking for surface mineralizations especially in sedimentary environments.

Hydro Geochemical surveys - in analyses for highly soluble and mobile chemical elements.

Bedrock Geochemical surveys - This is usually done during  the last stages of the exploration in order to confirm the mineralization.

Biogeochemical surveys - Although rarely used, in certain cases of mineralization, plants that grow in the area show certain characteristics that point to the mineralization - in the case of copper the leaves of a certain plant that grows in the vicinity turns to a brownish colour due to the absorption of copper.

Considering the conditions and expected methods of mineralization, a suitable geochemical exploration methods can be adopted if required along with geologic and geophysical methods in order to identify areas of mineralization.

An Introduction to Remote Sensing

Remote Sensing, like the name implies, means observing and gathering information of an object from afar. In this sense we humans perform remote sensing all the time with our eyes and ears, where eyes and ears are our remote sensing equipment. However when moving away from the basics and expanding the scope of observation, many factors become involved and remote sensing becomes a broad and detailed area of study. Incorporating all these ideas, a general definition for remote sensing can be given as,

"The art and science of obtaining information about an object without being in direct contact with the object"

Remote sensing is extensively used in observing the earth and the environment for various purposes. The most common application of remote sensing is done in mine development, disaster mitigation and large scale environmental studies. Depending on the application, the sensors and the type of radiation used, the method of recording and processing and the analysis of the data will differ.

The major components in remote sensing are,
- an energy source for illumination :- usually the sun or an artificial source of radiation.
- medium of travel for energy :- the atmosphere.
- sensor :- orbits in a satellite eg. Landsat, Quickbird
- receiver on earth :- gathers the data transmitted from the satellite.
- equipment for interpretation and analysis of data :- remote sensing software.

All remote sensing systems have four types of resolution. They are,
- Spatial resolution :- refers to the pixel resolution of the image produced.
- Spectral resolution :- refers to the range of EM radiation that can be detected. A broader range increases the scope of analysis.
- Temporal resolution :- refers to the orbital period of the satellite carrying the sensor. Faster the period, higher the resolution.
- Radiometric resolution :- refers to the differences of the intensity of radiation that can be distinguished by the sensor. Given as a bit range. A higher bit range can distinguish smaller variations.

Once all the above details are decided according to the application, remote sensing is performed. Then a "reflectance pattern" is produced from the gathered data. By comparing these patterns with the spectral signatures of known objects, the type and extent of the sensed objects on the earth can be inferred. In addition to various applications on earth, remote sensing is also used in other planets to gather data about surface conditions etc without landing on the planet.

Remote sensing in Mars. image form wikipedia

 

A Diamond is Forever

Gemstones have been objects of desire since ancient times and are commonly seen as symbols of wealth and prosperity. The field of Gemmology aims to identify, classify and add value to gem material. Of all the gemstones identified, the diamond holds a special place due to various reasons. While already being the most sought after gem stone, efforts companies like De Beers have increased the value of diamonds even more. An example is, the De Beers advertising slogan "A Diamond is Forever". This slogan increased diamond sales to such an extent that a diamond was a part of almost every engagement ring. It was coined by Frances Gerety and is regarded as the best advertising slogan of the 20th century.

The value of a gemstone usually depends on its beauty, rarity and hardness. Although these are very vague terms and beauty is not quantifiable, the factors that contribute to beauty are colour and clarity. In gemstones like aquamarine, value generally increases with colour intensity. In blue saphire, the value is highest at a particular colour, termed the "optimum colour". Clear gemstones without any intrusions or impurities are usually cut so that they are faceted. translucent, opaque or sometimes clear stones with intrusions are cut with a convex top and are called "cabochons". Even opaque stones can be valued highly due to properties such as Chatoyancy (cat's eye) eg- Chrysoberyl. and Asterism eg. Star saphire. Among so many varieties of stones the clear, faceted diamond is the most sought after.

The other factor that contributes to the value of a gemstone is its rarity. while gemstones are naturally rare, the demand for it creates an increase in value. However in some cases the rarity can be increased by the producers or traders of gemstones by stockpiling and controlling the release of gemstones to the market, like what De Beers did when they held the monopoly in the diamond business at a certain period of time. These practices however, rarely take place today. Hardness is the other key property of a gem quality material. A high hardness value means high durability and therefore it stands the test of time. Whether it's the case of beauty, rarity or hardness, the diamond clearly stands on top.

image from : wikipedia

Coastal Erosion at Beruwala

Some of the best beaches and coral reefs in Sri Lanka are located in the Beruwala area. The calm and clear waters around the large coral reef near hotel Chaaya Bay Beruwala (formerly known as Beach Hotel Bayroo) is a perfect spot for snorkeling.

Unfortunately this area has undergone severe coastal erosion and pollution. The water has become murky and not a lot of fish can be seen around the coral reef. The reason for coastal erosion in this area is not clear, but it could be due to illegal sand and coral mining.

Beach Nourishment could be a possible solution to this problem. Although not a permanent solution it can help mitigate the effects of erosion for a certain time period. In addition to this, steps must be taken to prevent illegal mining from taking place in the area.

Mining Asteroids

Industries based on space exploration have received a lot of attention lately. Companies are already in the process of introducing commercial spaceflights to the general public. Among these new "space age" industries, is a new start up called Planetary Resources that focuses on mining Asteroids. Although it seems like a far fetched idea, the recently founded company Planetary Resources claim that they have a plan. They also have got some serious investors like Larry Page, co founder of Google to back them.

Asteroids are found in abundance in space and contain vast quantities of valuable minerals and metals. Asteroids also contain large amounts of water in them. Being much smaller than planets, the minerals in  an asteroid are distributed evenly throughout the entire body of the asteroid, unlike in planets where the large gravitation causes the heavier minerals to sink towards the core of the planet. This makes it easier to mine because deep excavation will not be necessary to access the resources of an asteroid.

Although the idea of mining asteroids for useful resources has been around for quite some time, this is the first time that it is actually being attempted. According to Planetary Resources, the final goal of the company which is mining asteroids commercially will take about a decade to accomplish. Despite this fact the company is set to generate revenue during the process, even before the actual mining takes takes place. In fact, one of its co-founders has claimed that Planetary resources is already a "positive cash-flow company".

Planetary resources plans to mine asteroids in 4 stages. The first stage is the "Arkyd Series100" in which a set of space telescopes known as "Leo space telescopes" will be launched. These telescopes which will be in low earth orbit and will be used to gather data about asteroids. The telescopes can also be pointed at other objects in space such as the moon  and planets as well as the earth itself. This capability gives the company the opportunity to rent out these telescopes to universities and other private and government organizations for research purposes. This is one avenue the company aims to profit in.

The second stage is the "Arkyd Series 200" also known as the interceptor in which further developed telescopes will be stationed in a higher orbit to obtain better access to asteroids and to gather data. These telescopes will also be equipped with micro propulsion mechanisms enabling them to move into different positions.

The third stage - "Arkyd Series 300" AKA Rendezvous Prospector will incorporate swarms of spacecraft capable of communicating with each other to move on to more distant asteroids and obtain specialized data regarding constituents, size shape, rotation etc while orbiting the asteroid. The technology developed during this stage is expected to generate revenue for the company by providing means of inter-planetary space flight to interested parties such as NASA and other agencies.

The fourth and final Stage is the Asteroid Mining itself. Mining will also be done using swarming robots with the ability to communicate and coordinate like in the previous stage. Several technological challenges will have to be addressed in this stage. For example whether the the processing of mined material is done on site or brought to earth before being processed. Both these methods have their advantages and disadvantages depending on the mineral to gangue ratio in the mined ore. Furthermore asteroids being situated at quite a distance from the sun, exploiting solar energy would be difficult. This creates the need for improvement of existing solar technology or the use of some other energy source. In addition to the technological issues, the legal matters pertaining to mining from outer space will have to be considered.

Planetary Resources plans mainly to extract platinum group metals and water from asteroids. Extracting water from asteroids can be very useful in future manned spaceflights and space stations because taking water from earth will not be necessary. Also the chemical constituents of water, Hydrogen and Oxygen if separated can be used as fuel for the space craft as well. This could lead to fueling stations in space and ultimately reduce the cost of space flight significantly.

The founding of Planetary Resources has redefined the limits of possibilities in the field of energy and resources. If it turns out to be successful it is bound to be the beginning of a revolutionary and extremely profitable industry while opening the doors to colonization in space. Most importantly it will be a great achievement of the human race.

images from : planetaryresources.com

Satellite Altimetry

The seafloor is not a smooth and uniform place. It has as many topographical features as on land. From the Continental Shelf through to the continental slope, the continental rise, the abyssal plane, mid oceanic ridges, seamounts, guyouts and trenches the seafloor varies and plays a vital role in the dynamics of the planet. For this reason, the seafloor and its features are extensively studied. The topography of the ocean floor is given the name Bathymetry.

In order to map and study the bathymetry, several methods are used. The earliest method of doing this was to get depth measurements at different points in the sea and plot submarine contour lines using them. This was a tedious process. With the development of technology new methods such as, echosounding, multibeam methods and seismic refraction and reflection methods are used today. The latest method of mapping the seafloor is Satellite Altimetry.

Like the name suggests this method uses satellites in orbit to map the seafloor. These satellites measure the slight differences of the sea level, and not the depth. Then how can it be used to map the seafloor? The way it's done is, the slight changes in sea level actually represent the topography of the seafloor. The undisturbed surface of the ocean represents the geoid - the gravitational equipotential surface. This means that at seamounts and ridges where there is a higher mass and thus higher gravitation, The sea-level would be higher and places such as trenches where the relatively lower mass lessens the gravitation, the sea level would be lower. Therefore by measuring the differences in sea level, the bathymetric features can be identified. This bathymetric data is used to plot bathymetric maps as shown below

bathymetry of the the indian ocean