Underground mine and pit maps serve two purposes: immediate mining by delineation of grade and geotechnical problems; and deposit-scale exploration/mine expansion. For expedience, many underground mapping programs tend to concentrate on grade delineation alone, and by the time future reserves become an issue, appropriate data is no longer available. Effective underground mapping adds sufficient stratigraphic and structural information into the map as to allow exploration models to be developed that are based on a true understanding of the structural control of mineralisation. Too often we have seen situations where grade maps, interpreted as stratigraphic maps, have lead to entirely erroneous exploration models.
Mines and pits provide the greatest and most direct opportunity to understand the detailed structural control of an orebody, and the pay-off can be immediate in grade control, mine planning and production scheduling. However, for this to occur the mapping program needs to be predictive and accurate, and by informed geological staff rather than by grade control technicians.
As with many of the introductory modules, the course can be slanted towards different types of deposits or terranes, and can emphasise either structural mapping (Rod Holcombe; Tim Coughlin) or alteration mapping and sampling
Underground Mapping topics
- Know your product: What a mine map should like like; stratigraphic maps; bedding and fabric trace maps.
- Map projection: How, and when not to, project units and structures. The mapping datum.
- Don't map blind: understand the theoretical aspects of your structure and the tools required to define it
- Going armed: preparation for mapping; have a clear idea of what to expect every day
- Key mapping observations: distinguishing clearly between grade/lode contacts and stratigraphic contacts
- Mapping process: Initial structural/strat skeleton to final detail
- Consistency in labelling: maps are also databases
- Structural measurements: techniques, tools, and conventions
- The devil is in the detail: knowing what to measure and why
- Cross-sections: the best place for interpretation is on the spot
- Consider the 3-D picture: check the relationship of the final map with maps up and down the section
- Grade/structure relationship: an ongoing 3-D analysis
- Skepticism is healthy: treat every mapping session as a test of "the model"
- Oriented drillcore basics: getting the most from core