Mineral and Petroleum Exploration

Introduction

Exploration geologists want to find valuable metals and other materials, like oil, in the ground, which can some day be mined (or extracted).  The sources of the metals in the ground are called ore deposits, and in the case of oil, the sources are underground reservoirs, called oil fields.  The work of discovering an ore deposit or oil field is the branch of geology known as mineral exploration or petroleum exploration, respectively.  It is obvious why mankind endeavors to find ore deposits and oil fields.  Raw materials and energy sources are necessary for the lifestyle of a modern society.  The products we derive from these materials allow us to have tools and materials to build things, like our homes, and make things, like tools.  Machinery required to grow crops is for food is also made from metals which are mined from the earth.  

Our society  been involved in mineral exploration for a very long time, in fact as long as its existence.  The earliest man needed to make sharp stones for making weapons for hunting and defense.  Collecting ornamental stones of beauty has also been a pastime for a very long time.  In our current society, mineral resources and oil are needed for everything from cars to computers.   

Exploration geologists want to discover new ore deposits and oil reservoirs.  An area of interest, called an exploration project, goes through several stages.  Typically the project will begin with a compilation and analysis of available, previous data to judge the rough potential for economic deposits of a commodity.  An initial pass through the project area, or “reconnaissance”, may be conducted which will hopefully locate some general targets or “prospects”.   Follow up work is then done on these prospects to obtain more detailed information and narrow the scope of the targets.  Detailed geochemical and geophysical surveys are important methods during this stage.  Finally, a target will be selected for drilling, the ultimate test.  Drilling may begin with “exploratory” drilling of a few holes.  Then drill holes will be strategically placed to obtain a 3 dimensional model of the subsurface geology and evaluate the potential for mining.

Five units, each focusing on a major exploration method or category, are included in the module: 

Unit 1:  Geological Field Methods –  These methods employ basic data gathering and mapping skills.  Ore minerals and rock types and structures must be recognized and be noted in the field.  Gathering accurate location data is a very important aspect of this work.  Surface data is used to project features to the subsurface and interpret the subsurface geology.

Unit 2:  Geochemical Methods – These methods employ sampling of geological materials and testing for abnormally high or low values of elements.  Minerals are defined by their composition, so discovering the chemical makeup of a mineral is essential for identification.  Abnormally high or low values of elements may trace a path to a source of economic significance.  Simple field tests can be performed which can indicate qualitatively the general composition of a an unknown mineral.  Geochemical testing is also necessary to accurately delineate the boundaries of the material to be mined.

Unit 3:  Geophysical Methods – These methods measure the physical properties of minerals and rocks to suggest the presence or absence of economic mineralization or petroleum concentration.  Most important are the properties of magnetism, electrical conductivity and density.  The magnetic properties of minerals and rocks can be used for identification, and discrepancies in earth’s magnetic may indicate a concentration of valuable mineras.  Metallic minerals are generally very conductive, and therefore this property can also be measured to indicate the presence of economic minerals, particularly metallic sulfides.  The density is of course related to the mass of a substance and mutual gravitational effects.  Discrepancies in the earth’s gravity field also may indicate economic mineralization.

Unit 4:   Drilling Methods – Drilling methods utilize drill rigs to penetrate the subsurface and retrieve representative materials consisting of chips or core.  Drilling is the culmination of the exploration process and represents the last stage of development before mining.  Drill data is used to create a model of the underground geometry of mineralization or oil accumulation.

Unit 5:  Petroleum Exploration – All of the previously mentioned exploration methods are utilized for petroleum exploration, but are used in different manners because of the inherent differences between minerals (solid) and oil (liquid).  Geochemical methods are used to evaluate oil formation, composition and quality, and geophysical methods are used to locate underground structures conducive to oil accumulation.  Drilling ultimately defines the presence or absence of economic concentrations of oil.