Aurorite, argentian todorokite, and hydrous silver-bearing lead manganese oxide

Economic Geology
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Abstract

During a study of hypogene manganese minerals, three silver-bearing manganese oxides were identified in "black calcite" associated with silver ores at the Aurora mine (Treasure Hill), Hamilton, Nevada. Specifically these are: (1) argentian chalcophanite (aurorite) (Ag 2 Ba,Ca,Pb,-K 2 ,Cu,Mn (super +2) )Mn 3 (super +4) O 7 . 3H 2 O; (2) argentian todorokite (Ag 2 ,K 2 ,Ca,Ba,-Na 2 ,Cu,Pb)Mn 4 (super +4) O 9 . 5H 2 O; and (3) hydrous silver-bearing lead manganese oxide (Pb,Cu,Ba,Sb,Ag 2 ,Ca,K 2 )Mn 5 (super +4) O 11 . 5H 2 O. Based on the large concentration of silver in argentian chalcophanite (7.50% Ag 2 O) and the low zinc content (0.25% ZnO) this mineral is recognized as a new species and named "aurorite."Physical and optical properties, and chemical analyses of the three minerals are presented together with X-ray powder diffraction data for aurorite and argentian todorokite. All chemical analyses were done with the electron microprobe analyzer. Due to extremely small particle size and textural relations, no X-ray powder data were obtained for the hydrous silver-bearing lead manganese oxide. Associated minerals include cryptomelane, pyrolusite, birnessite(?), cerargyrite, native silver, quartz, and manganoan calcite. Although the general uniform dark color of the "black calcite" and apparent uniform distribution of the inclusions suggests contemporaneous formation, examination of polished sections at high magnifications shows a definite paragenetic sequence. Manganoan calcite is replaced by fine-grained intergrowths of cryptomelane, pyrolusite, birnessite(?), and cerargyrite. Native silver formed early and the silver-bearing manganese oxides formed late in the sequence; aurorite fills microfractures that cut through all other minerals.These three silver-bearing manganese oxides were recognized only at the Aurora mine, Hamilton, Nevada, although black calcite veins were studied from numerous areas in the western United States. The geologic features of silver-bearing black calcites are described by Hewett and Radtke in the preceding paper.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Aurorite, argentian todorokite, and hydrous silver-bearing lead manganese oxide
Series title Economic Geology
DOI 10.2113/gsecongeo.62.2.186
Volume 62
Issue 2
Year Published 1967
Language English
Publisher Society of Economic Geologists
Description 21 p.
First page 186
Last page 206
Country United States
State Nevada
City Hamilton
Other Geospatial Aurora mine
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