In areas where new gold deposits are being explored for, geologists use deposit models to help choose the most appropriate exploration techniques and interpret the data they find.
Gold is an element and so is identical no matter where it is found. However, the rocks, minerals and elements that occur with gold, as well as the shape and size of each deposit vary in each instance. Geologists have found similarities among gold deposits that allow their grouping into Types.
These Types, while based on empirical observation, are now thought of in terms of their ore-forming processes. Gold exploration is now moving from an empirical approach to a more ore-systems and process orientated approach. Gold deposit models are central to this ore-systems approach. By working with a deposit model an explorer is able to target particular locations and select specific methods that ultimately lead to a discovery. This is the current best-practice method of exploration, but is far from a sure thing. The whole exploration science remains somewhat of a dark art, but is making significant progress toward a more probabilistic, system-based discipline.
How A Gold Deposit Model Is Used To Explore
An analogy to using gold deposit models in exploration would be a hunter (ie. the explorer) in a jungle looking for a big-cat (e.g. the gold).
The hunter knows that to improve his chances he will not waste time looking in the desert, so stays in the jungle. By sticking to the jungle the hunter has already increased his chances of success.
This is analogous to a gold deposit model which indicates gold deposits of a certain type are found in a particular type of rock. The explorer is lead to look in this favorable rock type by the deposit model.
In the jungle, the hunter knows there are several types of big-cat. Each big-cat type lives in a slightly different part of the jungle – some in the trees, some the undergrowth, others along streams. To better fine-tune his search the hunter will concentrate on a particular type of big cat. The explorer will similarly focus attention within the favourable rock type to those areas most likely to host the gold deposit of the model being used. For example along certain fault intersections, around magnetic or gravity anomalies.
As the hunter focuses in on the particular niche environment of his prey, he will look for signs of it’s presence – whether it be tufts of fur, footprints, scats, or sounds that are particular to that big-cat species. The explorer will also know what specific signs are left by the gold deposit model in question. These will usually include particular mineral alteration types, or elements associated which with the gold but are more widely distributed than it (for example Arsenic, Mercury, Antimony).
The hunter will carry weapons and tools best suited to tracking and killing the target big-cat species. Exploration tools will be used based on their suitability in detecting the target model type through the characteristics mentioned (alteration type, metal association gravity or magnetic anomalies).
If in his search the hunter comes across signs of another type of big-cat he should be open and flexible enough to change strategy to take advantage of the evidence at hand. The explorer should not be so dogmatic in the search for a specific gold deposit type that she ignores positive evidence for other types of gold deposits or evidence that points to a gold deposit occurring in what would be an un-likely location.
If instead of a big-cat, the hunter finds a snake, then he should also exploit this opportunity, assuming that he has the skills to do so without wasting energy or risking death. If a gold explorer comes across a nickel deposit, she would obviously not ignore it. However, the skills needed to develop a nickel deposit vary greatly from that of gold and therefore the explorer would likely sell or at least partner with an experienced nickel miner/development company.
The hunter may end up finding and killing a different big–cat species than he originally began searching for. This is still a successful hunt, and he was no doubt helped by the original model despite the outcome varying. Similarly a gold explorer may find a gold deposit different to the model they had been targeting. The point is that by using a deposit model, a better chance of success is provided by focusing efforts rather than aimlessly wandering around hoping to stumble upon signs of a gold deposit.