GEOLOGIC MAPPING AND MINERAL RESOURCES

The recording of geologic information on maps has been an essential part of geology since the earliest days of the science. William Smith is widely credited with producing the first published geologic map in 1815 and this symposium celebrates both that historic achievement and the diverse types and uses of geologic maps that have developed over the centuries. This presentation will focus on the use of geologic maps in exploring for and developing ore deposits. Although there are many tools in the explorationist’s toolkit ranging from regional geochemical and geophysical surveys down to hand sample and microscopic descriptions of mineralogy and alteration, geologic maps remain central and essential to modern exploration practices.

Geologic maps for mineral exploration record a level of detail that is not always attempted for regional mapping or land management purposes. Outcrop maps show not only the interpreted distribution of rock types but also the exact location of individual outcrops on the ground. This can be critical for correlation with assay information, geochemical and geophysical surveys, and location of drill holes.

Some exploration-focused maps record multiple layers of information for rock types, primary and alteration minerals, oxide versus sulfide mineralogy, and structural information that may be too detailed for recording on a standard geologic map. This multi-layer style of recording geologic information is sometimes referred to as the Anaconda-style. Such multi-layer techniques can be adapted for specific types of exposures such as trenches, benches within an open pit mine, or 3-D exposures in underground mines. A further variation involves drill core, which typically is mapped in multiple columns for rock type, mineralogy, structure, assays, etc. on a drill log sheet. Such information can be recorded graphically, often with multiple colored pencils, or with digital codes that can be entered directly into computer databases and 3-D visualization programs.