Viable indicator minerals in surficial sediments for two major base metal deposit types: Ni-Cu-PGE and porphyry Cu

Indicator minerals are known for many types of base metal deposits but the high temperatures and pressures associated with magmatism and prograde metamorphism are needed to raise mineral density and grain size in order to produce diverse and abundant indicators. Therefore those base metal deposits that are associated with very large magmatic-hydrothermal systems have the most viable indicator mineral suites, in some cases sufficient to produce anomalies in surficial sediments comparable to the regional-scale anomalies associated with kimberlite fields. Two deposits of this type are Ni-Cu-PGE and porphyry Cu. Most sulphide mineral grains dispersed from these deposits are quickly degraded by weathering, increasing the dependence on more stable alteration minerals. The significance and properties of these minerals are described and examples of anomalies are shown for Ni-Cu-PGE indicator minerals in glacial till and post-glacial gravel in Canada and for porphyry Cu indicator minerals in nonglacial sheet wash gravel in Chile.