The Geochemistry of Quicksilver Mineralization. Magnetometer Examination of the Monte Cristo Magnetite-Ilmenite Deposits

Citation

Dreyer, Robert Marx (1939) The Geochemistry of Quicksilver Mineralization. Magnetometer Examination of the Monte Cristo Magnetite-Ilmenite Deposits. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/DYZ2-4H66. https://resolver.caltech.edu/CaltechTHESIS:01052012-135937897

Abstract

The geochemistry of quicksilver mineralization:

The investigation has involved a geochemical, petrographic, and spectographic study of quicksilver mineralization. It has been found that cinnabar can be deposited only from alkaline sulphide ion concentration which is, in turn, partially dependent on the alkalinity of the solution. Such alkaline solutions are capable of dissolving silica, but carbonate and alkaline earth ions cannot exist together in such alkaline solutions. Any carbonatization of quicksilver deposits must thus represent a stage in the period of mineralization distinct from the period of cinnabar deposition. However, silica is often deposited syngenetically with cinnabar and the relationship of cinnabar and silica (unlike that of cinnabar and carbonate) is so intimate that the cinnabar occurs, in some places, as an extremely fine dispersion throughout associated silica. Associated with quicksilver mineralizing solutions are small amounts of a number of heavy metals as iron, chromium, manganese, arsenic, antimony, gold, silver, copper, zinc, nickel, germanium, lead, and cobalt. Of these elements, copper, silver, cobalt, lead, and germanium are always differentially concentrated in the cinnabar and such differential concentrations as have been observed are independent of the geographical and geological location of the deposit and are likewise independent of the type of wall rock in which the deposit occurs. The varying shades of cinnabar coloration cannot be attributed to any spectrographically determinable concentrations of any elements nor to the total amount of impurity which is differentially concentrated in the cinnabar.

The cinnabar-bearing solutions gain access into the wall rocks through fractures and intergranular voids and the greater part of all cinnabar ores is the result of such open-space filling. When the openings become filled, however, the solutions are quite capable of replacing the adjacent wall rock. If the wall rock is out of equilibrium with the quicksilver mineralizing solutions, the adjustment of equilibrium and consequent precipitation of mercuric sulphide will be quite rapid.

Precipitation of cinnabar is caused primarily by relief of pressure, evaporation of solvent, and wall rock reaction. Except in ammoniacal solutions, a decrease in temperature will not cause precipitation. Dilution of solutions causes the precipitation of metacinnabar and colloidal mercury. Such dilution is probably responsible for the native mercury which is a common, minor component of many quicksilver deposits. Acidification will likewise precipitate metacinnabar, but not cinnabar. The infrequent occurrences of metacinnabar can best be explained by near-surface dilution or acidification of hypogene solutions. Insofar as temperature and alkalinity are concerned, pyrite or both pyrite and marcasite could be formed simultaneously with cinnabar of metacinnabar or both. However, where marcasite occurs with cinnabar alone (as is quite commonly the case), the marcasite has probably been deposited separately form the cinnabar. Since cinnabar (rather than metacinnabar) is deposited only from hot alkaline solutions and since oxidized mercury minerals are very rare, supergene deposition of cinnabar must be a very local and a very uncommon occurrence.

Some cinnabar darkens rapidly on exposure to sunlight and it is suggested that this darkening may involve the formation of a surficial layer of colloidal mercury in solid solution in the cinnabar.

Magnetometer examination of the Monte Cristo magnetite-ilmenite deposits:

Situated in the San Gabriel Mountains of Southern California is a large body of anorthosite which is associated a number of bodies of ilmenitic magnetite. During the summer of 1937, the E. I. duPont de Nemours Corporation obtained options on a group of properties thought to contain several such deposits. In connection with the exploration of the aforementioned deposits, the authors were employed as geophysicists to conduct a magnetic examination of the area. The data contained in this report was collected between August 9 and September 4, 1937. Mr. Dawson is, at the present time, continuing the magnetometer investigation and, in the light of the facts to be presented in the following pages, his work is being watched with considerable interest.

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