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Extensive, variable, and generally thick regolith is a major challenge to mineral exploration in regolith-dominated terranes. The landscape of the Mount Isa Inlier, NW Queensland, Australia, is the product of several episodes of complex weathering, erosion and sedimentation. Weathering profiles were studied from more than 100 drill holes along three traverses crossing the Lady Annie, Mount Kelly and Anthill sulfide deposits to assess the nature, lateral extent and thickness of the supergene Cu oxide mineralization. A typical regolith profile consists, from the base up, of saprock, ferruginous saprolite (Cu-oxide zone), kaolinitic saprolite and silcrete bands (leached zone), and a pedolith of mottled, lateritic duricrust and soil zones. Oxidation of sulfides (primarily pyrite) in host rocks has created an acidic pH gradient, mobilizing Fe, Mn, Cu, Mo, Zn, Co, Ni, As, Bi, In, Sb, Be, P, U and Cd. The acidic pH is buffered by calcareous lithologies of the host rocks, particularly in the vicinity of the primary sulfides at Lady Annie and Mount Kelly resulting in formation of thick, mushroom-shaped Cu oxide halo, in which Cu may reach > 15 wt.%. The Cu values decrease to < 500 ppm in the bleached kaolinitic saprolite and silcrete. Conversely, siliceous bedrock lithologies at Anthill act as a weak buffer to the acidic fluids; thus, Fe, Cu and other mobile elements are laterally dispersed from the sulfide ore body and precipitated at different lithological boundaries where they are buffered by carbonates. Therefore, thick kaolinitic saprolite and silcrete are formed over sulfide mineralization, particularly along faults. Ferruginous duricrusts marginal to fault-controlled sulfide mineralization are anomalous in Cu, Zn, Cd, Sb and Be, and thus can be used as useful medium in geochemical exploration. Gold, Ag, Pb and As are residually concentrated in pedolith and kaolinitic saprolite over the primary sulfide mineralization. Thus, these elements can be used effectively as pathfinder elements, particularly in truncated landscape, where pedolith is eroded and the exposed kaolinitic saprolite is depleted in Cu. Ferruginous soil (850–300, 300–80 and < 80 μm size fractions), lag (> 1.6 and > 7.6 mm) and termite mounds have been applied successfully as sampling media for Cu oxide exploration in Anthill. Soil and lag over sulfide mineralization are rich in Fe, As, Pb, Ag, Bi, In, V, U and Mo. The best response over sulfide mineralization is recorded in the > 7.6 mm ferruginous lag. However, broadest signature of well-defined Au, Bi and In anomalies are better detected using termite mounds than soil and lag. Successful use of soil in exploration for Cu oxide deposits in Mount Isa requires a genetic discrimination between residual and transported origin. [ABSTRACT FROM AUTHOR]

Abstract Elemental mass changes were calculated for 154 samples from four rock types around the Ann Mason porphyry-Cu-(Mo Au) deposit, Yerington district, Nevada. The purpose of these calculations was to investigate addition and depletion patterns in two-dimensional (2-D) map space. Mass changes in Ca, Mg, Na, P, Cu, Mo, As, Sb, Sr, and Pb from samples in the pre- to syn -mineralisation Yerington batholith vary systematically with lateral and vertical distance from the Ann Mason deposit. At the core of the Ann Mason deposit, Cu and Mo were strongly added (>10,000% relative to average protolith values), with restricted lateral mass addition halos around the deposit. Copper is depleted in wall rocks surrounding the deposit. Calcium and Sr were removed (up to 98% depletion) from parts of the deposit centre due to the destruction of calcic-plagioclase and other calcium-bearing minerals during potassic alteration. Calcium (up to 1570%) and Sr (up to 315%) were added outside the deposit and were concentrated around 4 km from the deposit centre where epidote alteration is most intense. Arsenic and Sb were removed from the deposit centre (up to 99% depletion) where silicate-mineral alteration assemblages dominate. Antimony shows an addition halo (ranging from 25% up to 1900%) that extends from the deposit centre 500 m laterally away, and correlates spatially with the increased abundance of pyrite that typically surrounds porphyry deposits. Epidote-altered samples of Shamrock monzonite from outside the Casting Copper skarn show addition of Ca (up to 196%), Sb (up to 1100%), and depletion of Na (up to −98%). Samples from the central part of the post-mineralisation Shamrock monzonite record lower mass changes in Mg, Ca, P, and Mo, compared to other parts of the batholith. Some samples from the northern contact of the Shamrock batholith exhibit addition of Ca (up to 554%), Sr (up to 504%), and depletion in Na (up to −98%). These samples are coincident with strong epidote alteration. Our results provide a rock-normalised geochemical map that reflects quantified element addition and depletion patterns, which is useful for interrogating geological processes at a regional scale. Although interpreting relative element addition and depletion in map space is possible using conventional immobile element ratio approaches, mass balance calculations provide the benefit of quantified results. Highlights • Addition and depletion of elements can be calculated using Grant's Isocon approach. • Results show significant chemical mobility associated with epidote alteration. • Calcium and Sr mobility are strongly correlated with epidote alteration. • Albite in sodic-calcic alteration domains does not always indicate Na addition. [ABSTRACT FROM AUTHOR]