Indicator and pathfinder minerals can be used in mineral exploration to effectively narrow down the search area for many different types of ore deposits. Most commonly, indicator minerals are used in the search for diamonds, gold, nickel-copper deposits, platinum group metals, porphyry copper deposits, massive sulfide deposits, and tungsten deposits.
Indicator minerals are mineral species that, when found as grains within sediments and/or rocks, give clues as to the possible presence and location of specific types of mineralization.
In indicator mineral-based exploration programs, sediments and rocks are either geochemically tested or visually inspected for clues into the distance and direction to their source. When it comes to visually inspection, rocks are examined for certain grain morphologies and surface textures in order to obtain information about transport distance and bedrock source. The gold exploration branch in this area has matured into a distinct exploration tool, known as Gold Grain Morphology.
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Click here to access an INN Insider’s Report on gold investing (value: $49) – For FREE. Limited time offer. No credit card required.Gold Grain Morphology makes use of the fact that, over time, through contact with water, wind and precipitation, all rocks undergo physical and chemical changes through a process called weathering. Weathering may eventually lead to erosion, which occurs when a rock is weathered enough that it breaks off from its “host” rock and then is transported to a new local.
Every mineral has a unique resistance to this process. For example, gold’s resistance to the physical weathering processes is low.
On the other hand, chemically inert gold is resistant to chemical weathering. Therefore, while gold grains are physically altered, and often transported to new locations, the chemical nature of gold does not change.
Gold grains themselves can provide insight into the bedrock location of a valuable gold deposit. In fact, gold grain abundance and grain characteristics have been applied systematically in the past 35 years in the search for sources using the size, shape and chemical compositions of rocks with gold.
In short, gold grain morphology uses the weathering of the metal as a means to classify gold grains and narrow down their distance from source. In 1990, R.N.W. DiLabio devised a classification scheme in which gold grains are classified into three categories: pristine, modified and reshaped.
For pristine gold grains, the primary shapes and surface textures of the grains are preserved. In modified gold grains, some primary surface textures are preserved, however, but some edges and protrusions have been damaged during transport. For reshaped gold grains, the primary surface textures are destroyed and the original grain shape is no longer discernible.
By taking multiple samples of sediment, and classifying the gold grains according to the above scheme, the search area for a source of gold in an area can be narrowed down.
Composition studies
In composition studies, grains of particular pathfinder minerals are recovered and visually examined (similar to gold grain morphology) to obtain information on transport directions and distances. Geochemistry is often used in this step, in order to confirm the mineral’s identity. Compositional studies identify different populations within/between samples and potential bedrock sources.
Compositions most commonly characterized in gold exploration include gold, silver, platinum, palladium, copper, mercury, lead, iron, and tellurium.
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Furthermore, inclusions of other minerals within gold grains can provide insight into the ore and gangue minerals present in the bedrock source of the gold. This can provide exploration geologists with clues as to the deposit type and associated mineralization.
For example, enargite inclusions may indicate a high sulfidation epithermal source, while argentite inclusions may indicate mesothermal gold.
While inclusions can provide valuable insights into deposits types and even their possible location, inclusions are often easily eroded from the gold through transport. Thus, they are often only useful when found in close proximity to the bedrock source.
Geochemical pathfinders
Pathfinder minerals are minerals that often formed in close association with gold. Therefore, their presence, even in seemingly gold-barren rock, opens up the possibility of locating a nearby gold deposit.
Geochemical pathfinders are an important tool in gold exploration. Due to the fact that gold is so rare, locating it in a sample is very unlikely. Through the identification of pathfinder minerals, explorers can help determine the possibility of gold occurrence in a given area.
Examples of pathfinder minerals that are geochemical indicators for gold include: silver, copper, lead, zinc, cobalt, nickel, arsenic, antimony, tellurium, selenium and mercury.
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“Is The New Gold Era Upon Us?” Discover what the global elite doesn’t want you to know.
Click here to access an INN Insider’s Report on gold investing (value: $49) – For FREE. Limited time offer. No credit card required.This article was originally published on Gold Investing News on June 6, 2011.
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