Earth Resources : Mineral Resources , Water Resources & Energy Resources

Mineral Resources

Mineral Deposits

Metallic resources are those minerals that contain metals in their chemical composition (a product obtained when the mineral was melted). These usually have bright and metallic luster. Examples include iron ore, chromite and bauxite.

Non-metallic resources such as sand, gravel, gypsum, halite, talc, are those resources that do not yield new products when melted. These do not have metallic luster.

There are many geologic processes involved in the rock cycle that plays a major role in the accumulation and concentration of valuable elements / minerals.

1. Magmatic Ore Deposits

These deposits are substances concentrated within an igneous body through magmatic processes such as crystal fractionation and crystal settling.  These magmatic processes concentrate the ore minerals having the valuable substances that were widely dispersed and in low concentrations within the magma.

Crystal settling . The early crystallization and settling of heavier minerals at the lower portion of the magma chamber as magma cools down. 

Examples are Chromite (FeCr2O4), Magnetite (Fe3O4) and Platinum (Pt).

Fractional crystallization . The residual melt from separated component favors the formation of pegmatites which may be enriched in Lithium, Gold, Boron or large crystals of quartz, feldspars and muscovite.

2. Hydrothermal Ore Deposits

These are substances by concentrated through hot aqueous (water-rich) fluids flowing through fractures and pore spaces in rocks. These hydrothermal solutions can dissolve valuable substances (at low concentrations) from rocks. When the metal enriched hot waters move into cooler areas the dissolved substances precipitate into solid forms.

• Vein type deposits (in fault or fissure openings or in shear zones ) has most productive deposits of gold(Au), silver(Ag), copper(Cu), lead(pb) , zinc(Zn), and mercury(Hg).

• Disseminated deposits (large volumes of rocks) for porphyry copper deposits

• Massive sulfide mineral deposit (at oceanic spreading centers or ridges) such as sphalerite (ZnS) and chalcopyrite (CuFeS2)

.• Strata bound ore deposits (in lake or oceanic sediment) forms minerals such as galena (PbS), sphalerite (ZnS) and chalcopyrite (CuFeS2).

3. Sedimentary Ore Deposits

A type of deposit of valuable substances concentrated through chemical precipitation from lakes or seawater.

The most commom are evaporite deposits (in closed marine environment) that precipitate halite (NaCl), gypsum (CaSO4∙2H20), borax (used in soap), sylvite (KCl), hematite and magnetite.


4. Placer Ore Deposits

These are deposits of valuable substances concentrated through gravity separation during sedimentary processes. In these process, the heavy minerals are left and concentrated by water currents and the less-dense particles remain suspended and are carried further downstream.

Common placer ore deposits are gold, platinum, diamonds and tin.

5. Residual Ore Deposits

 An accumulation of valuable substances through chemical weathering processes wherein the volume of the original rock is greatly reduced by leaching.

Common deposits are bauxites (the principal ore of aluminum ) and
nickeliferous laterites or nickel laterites (mixture of the insoluble nickel, magnesium and iron oxide ).
Lesson 4.2 – Mineral Exploration

Mineral exploration follows the well-defined stages. The steps below are for general exploration projects wherein the activities may be different based on the type of mineral being explored.

1. Project Design

This is the initial stage in formulating a project. This involves review of all available data (geologic reports, mining history, maps, etc.), government requirements in acquiring the project, review of social, environmental, political and economic acceptability of the project, and budget and organization proposals.

2. Field Exploration

This stage involves physical activities in the selected project area. This can be subdivided into three phases:

a. Regional Reconnaissance
The main objective is to identify targets or interesting mineralized zones covering a relatively large area (regional). In general, the activities involve regional surface investigation and interpretation.

b. Detailed Exploration
This involves more detailed surface and subsurface activities with the objective of finding and delineating targets or mineralized zones.

c. Prospect Evaluation
The main objective is to assess market profitability by
(1) extensive resource, geotechnical and engineering drilling
(2) metallurgical testing and
(3) environmental and societal cost assessment.

3. Pre-production Feasibility Study
The feasibility study determines and validates the accuracy of all data and information collected from the different stages. The purpose is for independent assessors to satisfy interested investors to raise funds and bring the project into production.
     
Mining Methods

1. Surface Mining
This mining is used to extract ore minerals that are close to Earth’s surface. The different types include open pit mining, quarrying, placer mining and strip mining.

Open pit mining creates big hole in the ground from which the ore is mined.

Quarry is a type of open pit mine usually associated with the mining of non-metallic resources such as limestone, sand and gravel.

Placer mining uses water to excavate, transport, concentrate, and recover heavy minerals from alluvial sediments or placer deposits.

In Strip mining method, ore is removed or extracted in strips. This involves removing the top layer of soil instead of digging deep holes.

2. Underground Mining

This method of mining is used to extract ore minerals that is deep under the Earth’s surface.

The Milling Process

The materials extracted or “mined" are rocks composed of both ore and waste material. Waste materials are part of the rock which contain very little or no element or mineral of economic value.  The rocks that were extracted will further undergo processes of mineral (e.g. metal) separation and recovery through some processes usually done in a mill.

Initial Stage

The initial stage involves crushing and screening for controlled size reduction followed by grinding where the rocks are pulverized.

1. Heavy media separation

The crushed rocks are submerged in liquid where the heavier/denser minerals sink thus are separated from the lighter minerals. This is commonly used to separate chalcopyrite from quartz before the refining processes of extracting copper.

2. Magnetic separation

If the metal or mineral is magnetic, the crushed ore is separated from the waste materials using a powerful magnet.

3. Flotation

The powdered ore is placed into an agitated and frothy slurry where some minerals and metals based on physical and chemical properties may either sink to the bottom or may stick to the bubbles and rise to the top thus separating the minerals and metals from the waste.

4. Cyanide heap leaching

This method used for low-grade gold ore where the crushed rock is placed on a “leach pile” where cyanide solution is sprayed or dripped on top of the pile.

As the leach solution percolates down through the rocks, the gold is dissolved into the solution. The solution is processed further to extract the gold.

The waste material is either used as a backfill in the mine or sent to a tailings pond, while the metals are sent for further processing.

Environmental Impacts

There are several possible environmental impacts of irresponsible mining. Improper mining can cause flooding, erosion, subsidence, water and air pollution, damage to wildlife and habitat.

These are some of the measures that may prevent or mitigate the harmful effects of irresponsible mining:

1.) Topsoil replacement using uncontaminated soil
2.) Reintroduction of flora and fauna
3.) Neutralizing acidic waters
4.) Backfilling and sealing of abandoned underground mines
5.) Stabilizing the slope of impacted area to reduce erosion
6.) Promote environmental awareness and protection in relation to mining.

Energy Resources

Energy

Energy is a very important resource for human consumption. It has many uses in the field of Agriculture, Transportation, Residential, Commercial and Industrial purposes. 

There are also various energy sources which can be classified into two broad categories:

Non-Renewable Sources
1. Coal
2. Oil
3. Natural Gas
4. Nuclear
Renewable Energy Sources
1. Solar
2. Wind
3. Hydroelectric
4. Biomass
5. Geothermal

Types of Energy Resources

A.) Fossil Fuels

Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of dead organisms that have been buried for thousands or millions of years and mostly contain high amounts of carbon. These energy resource include coal, natural gas, petroleum and other fuel derivatives such as kerosene and propane.

1. Coal

Coal is a very combustible black or brownish-black sedimentary rock formed in layers of rock strata in layers or veins referred to as coal beds or coal seams.

It is composed mainly of carbon and with smaller amounts of other elements such as hydrogen, oxygen, sulfur, and nitrogen.

The Different Types of Coal

Anthracite contains 86 to 98% pure carbon with 8 to 3% volatile matter. It is widely used as fuel heat homes.
Bituminous coal has 70 to 86% carbon with 46 to 31% volatile matter. It is used to make coke, used in metallurgy.
Sub-bituminous coal contains 70 to 76% carbon and with 53 to 42% volatile matter. It is primarily burned in industrial boilers.
Lignite has 65 to 70% carbon with 63 to 53% volatile matter. It is considered a low-grade fuel due to its high moisture content and it is mainly used in industrial boilers.
Peat is formed from partially decomposed vegetation. It is considered a poor fuel due to the low carbon content of less than 60% and it is composed entirely of volatile matter.  It was used for cooking, domestic heat and few industries.

2. Petroleum

Petroleum is a naturally occurring fossil fuel formed by the decomposition of organic matter beneath the Earth's surface over millions of years . It is a yellowish-black liquid that may be refined into various types of fuels.

The refining of petroleum is carried out in an industrial process plant wherein the crude oil or petroleum is refined or transformed into more useful products such as liquefied petroleum gas, heating oil, gasoline, petroleum naphtha, kerosene, jet fuel, diesel fuel, fuel oils, and asphalt (bitumen).

3. Natural gas

Natural Gas is a fossil fuel energy source that was formed deep beneath the earth's surface and often with or near petroleum deposits.

Natural gas is a mixture of several hydrocarbons and consists mainly of methane.  It also has lesser contents in varying amounts of butane, propane, ethane, and nitrogen.

Fossil Fuel  Power Generation

Steam turbines may be used to extract thermal energy from the fuel. The steam is converted to kinetic/mechanical energy. Then a rotary generator is used to further convert it to electrical energy.

B. ) Geothermal Energy

Geothermal energy is a clean and sustainable form of energy generated from the thermal energy contained in the earth. This renewable energy source  can be used directly to supply heat or may be converted to mechanical or electrical energy.

C. Hydroelectric Energy

Hydroelectric energy is a form of renewable energy resource that harnesses water stored in dams, water flowing in rivers and lakes, as well as waves, tides and currents to create electricity.

Hydropower plants are the world’s leading renewable energy source, producing 83% of renewable power.  Inside hydropower plants, rotating blades spin a generator that converts the mechanical energy of the spinning turbine into electrical energy.

Water Resources

Water

Water is a simple compound that is very important to life and has remarkable and useful properties. Many scientists believe that, the presence of water made life possible to exist on Earth.

Distribution of Water on Earth

Water is the considered as the most abundant substance on the surface of the Earth and nearly all ( at 97.5% ) of the Earth's water can be found in the oceans. This leaves only a small portion ( at 2.5% ) is freshwater.

Most of the freshwater locked as ice in the wide glaciers of Greenland ( 68.7% ), a small portion at permafrost (0.8%), and 30.1% as groundwater. This means, there is only 0.4% of freshwater available for humans use.

The rest of the freashwater can be found in lakes  (67.4%), rivers and streams (1.6%), wetlands (8.5%) and in the atmosphere as water vapor (9.5%). Others are present in plants and animals (0.8%), and in soil moisture (12.2%).

Our knowledge of how water cycles through the environment helps us in determining the amount of water available in different parts of the world. This is referred to as the Earth’s water cycle ( or Hydrologic Cycle ). It is the global mechanism by which water moves from the air to the Earth and eventually back to the atmosphere.

Movement of Water through the Cycle

Approximately 40% of precipitation comes from previously evaporated water from the oceans while the rest from different parts of the land. Around the world, the amount of this precipitation may vary greatly. In desert climates, it may only be less than 100 mm a year, but in tropical settings precipitation rises to over 3,400 mm a year.

In temperate climates, about one-third of precipitation returns to the atmosphere through evaporation, the other third filters into the ground and adds to the groundwater and the rest flows into water bodies.

In drier climates, there is a higher the proportion of precipitation that returns to the atmosphere and lower proportion replenish the groundwater.