The deposits contain the important silver ore minerals, argentite and pyrargyrite
, as well as argentiferous galena and antimonial silver minerals, the latter in their deeper portions.
Similar pearceite specimens have trickled out before from the huge silver mine, but these new pieces display very brilliant rosettes, some with attachments of bright red, pinwheel-shaped aggregates of what is probably proustite (Luis's labels call it pyrargyrite
, but proustite seems more likely, as the Uchucchacua orebody is arsenic-heavy, and the association here is with As-rich pearceite, not Sb-rich polybasite).
Another less important Ag mineral is pyrargyrite
(called 'ruby silver' by prospectors), which was only abundant in the Silver King, Husky, Elsa and, particularly, the Lucky Queen mines.
Silver occurs in the galena, as electrum, and in tetrahedrite, argentite, and pyrargyrite
Its ore was chiefly pyrargyrite
, called "rosicler" by the Spaniards.
Mineralization is known over a vertical range of 500 m and consists of sphalerite, galena, chalcopyrite, tetrahedrite-tennantite, pyrite, wolframite, and pyrargyrite
in a gangue of quartz, calcite, siderite and rhodocrosite.
In the first decade of the 20th century, the Las Chispas mine near Arizpe in Sonora produced some of Mexico's largest and best specimens of polybasite crystals, large clusters of "poker chip" stephanite crystals, fine acanthite crystal clusters and a few very fine pyrargyrite
Since the turn of the century, fantastic specimens of wulfenite, calcite, amethyst, pyrargyrite
, acanthite, galena, gypsum--the list goes on and on--have made their way to collections across the globe.
The principal minerals found are argentite, aguilarite, naumanite, and guanajuatite, and it has been shown that contaminants such as arsenic, selenium, and antimony decrease with depth; thus minerals such as pyrargyrite
and proustite also become rarer as mining goes deeper into the Earth.
During the 1890s and the first few years of the 20th century the Las Chispas mine near Arizpe produced some of the world's finest specimens of polybasite, pyrargyrite