Jean-Francois Carpentier's Blog
Neyite and Unnamed Bi-Pb-Hg-Ag-Cu sulfosalt from Outlaw mine
24th Feb 2008
Some years ago, I obtained a small specimen from the former collection of Dr. Hans-Jürgen Wilke, labelled as “Benjaminite” and coming from the Outlaw Mine, Round Mountain District, Nye Co., Nevada, USA (Type locality for Benjaminite). This specimen consists of inclusions to 4 mm of grey metallic Cu-Bi sulfosalts in milky Quartz matrix. I had aliquots of this specimen analyzed by semi-quantitative SEM-EDX and found that it does indeed contain a phase that fits what is expected for Benjaminite, but also other phases, intimately mixed with Benjaminite, namely Aikinite (the major ore mineral at this locality), but also Neyite (which was not reported so far to my knowledge), and a Bi-Pb-Hg-Ag-Cu phase (likely a new mineral species but not appropriately described so far), refers as to "Unnamed sulfosalt 1" in Mindat.
For those interested I post here the EDX results of this - what I think is - interesting specimen:
Bi-Pb-Hg-Ag-Cu phase
[results of my EDX (average of 5 spots): Cu 0.95; Hg 7.78; S 14.80; Pb 33.67; Bi 38.52; Ag 4.30; total 100.00 wt.%]
this composition is closely related to those previously described as “Unnamed sulfosalt #1 = Phase X, results of 2 analyses: Cu 1.3, 1.3; Hg 8.3, 8.4; S 15.9, 16.0; Pb 29.8, 29.3; Bi 40.3, 40.6; Ag 3.4, 3.6; total 99.3, 99.3 wt.%, which corresponds to an average composition (Hg2.23Ag1.40Cu1.05Pb0.32)(Pb)8.0(Bi10.71Mo0.06Pb0.05Sb0.02) and Unnamed sulfosalt #2 = Phase Y: results of 2 analyses: Cu 1.60, 1.61; Hg 10.13, 9.14; S 15.40,15.42; Pb 35.04, 34.71; Bi 36.79, 36.95; Ag 2.59, 2.43; total 101.61,100.37 wt.%”
Neyite
ideal formula is Pb7(Cu,Ag)2Bi6S17; Bi/Pb = 1.17
average formula calculated on 5 spots: Pb7(Cu1.1.,Ag1.3)sum=2.4Bi6.5S17.1; Bi/Pb = 1.08
For an adequate reference to this complex Bi-Pb-Hg-Ag-Cu chemistry at Outlaw, see:
Coexisiting GalenaA, PbSo and Sulfosalts: Evidence for Multiple Episodes of Mineralization in the Round Mountain and Manharan Gold Districts. Nevada; E.E. Ford, D.R. Shawe, N.M. Conklin, Canad. Miner. 1988, 26, 355-376).
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Thanks for the info on the Outlaw mine. I had not noted Neyite there but that is not unusual with the complex sulfosalt mineralogy of that very small outcrop. Please see our article in Min Rec on the mine, Vol 22, 1991 which gives some photos of the remote mine. Yes, you have found one of the two unknown minerals remaining at the mine. And, yes the majority of the visible sulfosalt is aikinite. The benjaminite seems to be rather illusive but it is there if searched closely.
Good hunting,
Gail Dunning
Mr. Gail E. Dunning
10th Mar 2008 4:18pm