Exploration of a Gold deposit involves a series of systematic steps in converting a mineral occurrence into
- Firstly a Mineral Prospect (indication of gold mineralisation supported by assays, width and length)
- Then a Mineral Resource (Three dimensional exploration through drilling to indicate possible tonnage and grade)
- and finally Mineable Ore reserves (completion of feasibility study and mine development to estimate proven tonnage and grade)
The Gold Exploration process involves :
- Literature Survey
- Use of Modern Exploration Methods
- Pre-Feasibility Studies
- Feasibility Studies
A. Literature Survey
India has a long history of mining for gold, dating back to 2000 years. References pertaining to old mine sites are available from the records and reports published by a number of British mining companies which were actively involved in exploration and mining of gold from the year 1880 onwards. After Independence, the Geological Survey of India (GSI) has carried out extensive regional exploration for gold in different parts of the country. Similarly, the Mineral Exploration Corporation of India (MECL) has conducted detailed surface and underground exploration for gold in deposits identified by GSI. In addition to these two Central Government agencies, the State Directorates of Geology & Mining located across the country have also contributed to gold exploration. The geological and exploration data generated by all these agencies are available in several publications of respective agencies. A collection of all this literature which facilitates picking up of targets for further probing, forms the first step in exploration process.
B. Use of Modern Exploration Methods:
The modern exploration techniques include but are not restricted to carrying out a study of remote sensing data such as landsat imagery, Aster and Hyperspectral data, Airborne geophysical surveys using magnetics, gravity, electro magnetic and seismic techniques, Regional and detailed geological and structural mapping of various rock types and associated geological structures controlling mineralization, Sampling of surface outcrops to understand if there are any anomalous concentration of minerals/metals, Regional and detailed geochemical surveys including sampling of stream sediments, different layers of soil, rock, water, plants, termite mounds etc to identify possible targets and geochemical patterns associated with the mineralised zones, Multi parametric ground Geophysical exploration techniques such as ground magnetics, Induced polarization, Gravity, Seismic, Radiometric, Resistivity Surveys, Trenching to expose the concealed mineralised zones, Drilling including diamond core, Reverse Circulation, RAB, Trenching and multi element chemical analysis. The exploration results culminate with drilling to understand the 3rd dimension of the mineralised zones, and data processing using 2D and 3D geological softwares to define the 3D ore body model and Resource estimation.
There are different methods or standards adopted for Estimation and Reporting of Mineral Resource and Reserves internationally, such as JORC, CIM and UNFC (adopted by MoM, Government of India). The following links provide details of these standards:
Exploration is now supported by a variety of advanced data integration and processing tools, from advanced 2D GIS platforms, which have the ability to display drilling data, to full blown 3D data modeling, processing and visualization packages.
Finally, people are the backbone of any good exploration approach. Not only do team members need to have the ability and experience, they must also understand the characteristics of the gold deposits they are searching for and be given sufficient field time to adequately test their targets.
Other factors such as an excellent understanding of proven exploration methods, effective use of technology, enthusiastic and responsible leadership, confidence in corporate direction, and attracting and training young professionals, are also important.
C. Pre-Feasibility Studies:
A Pre-Feasibility Study is a comprehensive study of the viability of a mineral project that has advanced to a stage where the mining method, in the case of underground mining, or the pit configuration, in the case of an open pit, has been established, where an effective method of mineral processing has been determined, and includes a financial analysis based on reasonable assumptions of technical, engineering, legal, operating and economic factors and evaluation of other relevant factors which are sufficient for a Competent Person, acting reasonable, to determine if all or part of the Mineral resource may be classified as a Mineral Reserve.
D. Feasibility Studies:
A Feasibility Study is a comprehensive study of a mineral deposit in which all geological, engineering, legal, operating, economic, social, environmental and other relevant factors together with operational factors are considered in sufficient detail. The results of the study may reasonably serve as the basis for a final decision by a proponent or financial institution to proceed with, or finance, the development of the project. The confidence level of the study will be higher than that of a Pre-Feasibility Study.