Study of Zn-bearing beaverite Pb(Fe_2Zn)(SO_4)_2(OH)_6 obtained from Mikawa mine, Niigata Prefecture, Japan

摘要

Zn-bearing beaverite occurs as a secondary mineral in an oxidized zone of a quartz vein in the hydrother-mal Cu-Zn-Pb ore deposit of the Mikawa mine, Niigata Prefecture, Japan. The Zn-bearing beaverite is dark brown in color with streaks and the associated minerals are quartz, galena, sphalerite, pyrite, anglesite, beaverite, orthoclase, and osarizawaite. The empirical formula of the mineral based on EPMA is Pb_(0.95)(Fe_(1.88)Al_(0.10)) _(Σ1.98)(Zn_(0.83)Cu_(0.30))_(Σ1.13)(SO_4)_2[O_(0.38)(OH)_(5.36)]_(Σ5.74) for S = 2, which leads to the ideal formula Pb(Fe_2Zn)(SO_4)_2(OH)_6. The crystal structure is refined by Rietveld analysis in the space group R3m. Using powder XRD data obtained by the combined use of a Gandolfi camera and monochromatic synchrotron radiation, the following values are obtained: a = 7.3028(2), c = 17.0517 (4) A,V= 787.56(4) A~3, and D_(ealc) = 4.25 g/cm~3.