An archived series of papers by R. W. Boyle:
On Antimony for Geochemical Prospecting:
The geochemistry of antimony is reviewed, and the use of the element as an indicator in geochemical prospecting for various types of mineral deposits is outlined. Antimony is widely diffused in many types of mineral deposits, particularly those containing sulfides and sulphosalts. In these and other deposits, antimony commonly accompanies Cu, Ag, Au, Zn, Cd, Hg, Ba, U, Sn, Pb, P, As, Bi, S, Se, Te, Nb, Ta, Mo, W, Fe, Ni, Co , and Pt metals. Under most conditions antimony is a suitable indicator of deposits of these elements, being particularly useful in geochemical surveys utilizing primary halos in rocks, and secondary halos and trains in soils and glacial materials, stream and lake sediments, natural waters, and to a limited degree vegetation. Some of the natural antimony compounds (e.g. stibine, dimethylstibine) are volatile, but methods utilizing gaseous antimony halos for geochemical prospecting have not yet been developed.
On Silver for Geochemical Prospecting:
The general geochemistry of silver is briefly discussed, followed by summary descriptions of the common types of argentiferous deposits and brief discussion of the world production of the metal. A short section on the origin of argentiferous deposits completes the paper, The epigenetic vein, lode, stockwork and disseminated types of argentiferous deposits originated mainly by metamorphic secretion and/or granitization processes, the source rocks of the silver and its associated elements being mainly in the enclosing volcanic and/or sedimentary piles. Many of the native silver-Ni-Co arsenide veins appear to represent late secretion extracts derived probably by diffusion from a variety of rnetal-rich rocks such as graphitic, pyritic sediments, volcanics, and diabase sills as at Cobalt, Ontario. The 'red bed' type silver deposit ts are epigenetic in origin, the silver and accompanying elements being derived from a variety of sources such as underlying metalliferous shales and volcanics. In places the red and black beds of the 'red bed sequences' may be the source of the silver and its associated elements. The argentiferous copper shales (Kuperschiefer type) have a sedimentary signature, but the rich Cu-Ag sections (shoots) appear to have been concentrated from the body of the shales by diagenetic and/or metamorphic fluids.
The oxidation processes in silver deposits are complex and depend essentially on the Eh and pH. Colloidal and coprecipitation phenomena also play a large part. Iron and manganese minerals and carbonates in the gangue and ore greatly influence the reactions that lead to the secondary enrichment of silver. The common supergene minerals of silver are the various halides (chlorargyrite, bromargyrite, iodargyrite) and argentojarosite in the zone of oxidation of argentiferous deposits, and native silver, pyrargyrite, proustite, and argentiferous chalcocite in the zones of reduction.
Most of the world's production of silver 11,500 metric tons) is obtained as a byproduct of copper-silver shale deposits, various types of polymetallic deposits enriched in Pb, Zn, and Cu, gold deposits, Ni-Cu deposits, and porphyry Cu-Mo deposits; a small production «5 percent) comes from native silver-Ni-Co arsenide sulphide deposits.
On Gold for Geochemical Prospecting:
The general geochemistry of gold is briefly discussed, followed by summary descriptions of the common types of auriferous deposits and a brief discussion of the world production of the rnetal. A short section on the origin of auriferous deposits completes the paper. The epigenetic vein, lode, stockwork and disseminated types of gold deposits originated mainly by metamorphic secretion and/or granitization processes, the source rocks of the gold and its associated elements being mainly in the enclosing volcanic and/or sedimentary piles. Modern gold placers are of sedimentary origin, the gold being winnowed into pay streaks as the result of both chemical (accretion) and physical (gravity) processes operating during weathering and subsequent sedimentation. The auriferous quartz-pebble conglomerate deposits probably originated as placers, the gold and many of its associated elements having undergone radical chemical re-working during subsequent diagenetic and metamorphic events.
On Blind Mineral Deposits Prospecting:
Part 1 of this paper, published in the August issue, covered lithochemical surveys based on major, minor and trace elements in whole-rock samples from primary enveloping halos.
Part 2, which follows, continues with discussions of surveys based on leakage halos, zonatian of elements, stable and radioactive isotopic distributions, and geothermometric, geobarometric, thermoluminiscent, pedochemical, hydrochemical, atmochemical and biogeochemical methods. It concludes with a selected bibliography.
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