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A STUDY OF Au-Cu MINERALS USING THE ELECTRON PROBE
S. Mao, Yehan Liu
To cite this version:
S. Mao, Yehan Liu. A STUDY OF Au-Cu MINERALS USING THE ELECTRON PROBE. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-631-C2-634. �10.1051/jphyscol:19842147�. �jpa-00223818�
JOURNAL DE PHYSIQUE
Colloque C2, supplément au n°2, Tome 45, février 1984 page C2-631
A STUDY OF A u - O u MINERALS USING THE ELECTRON PROBE
S.H. Mao and Y.X. Liu*
Department of Earth Sciences, University of Cambridge, U.K.
Institute of Comprehensive Utilization of Mineral Resources, China Résumé - On a analysé un certain nombre de granules de minéraux Au-Cu, pro- venant d'un dépôt de cuivre-nickel sulfurisé du nord-ouest de la Chine. On y a trouvé quatre espèces. Celles-ci sont : AuCu, AuCuo, AU3CU2 et Au presque pur, contenant un faible pourcentage de Cu. D'après la composition chimique nous montrons que AU3CU2 est un nouveau minéral.
Abstract - A number of grains of Au-Cu minerals, which are from a sulphurised copper-nickel deposit in North-West China, have been analysed and four species have been found. They are: AuCu, AuCu3, Au3Cu2 and nearly pure Au containing a few percent of Cu. According to the chemical composition we considered that Au3Cu2 is a new mineral.
INTRODUCTION
The unit cell of copper is smaller than that of gold, so Au and Cu can only form solid solution at high temperature and unmix on cooling. Hansen & Anderko (1958), Barrett & Massalski (1966) reviewed the constitution and structure of Au-Cu alloys respectively. According to the references they quoted, there are several different phases with the following composition and structure: AUCU3 (cubic), AuCu I (tetra- gonal), AuCu II (orthorhombic), Au3Cu (cubic) and probably Au2Cu3. Heinrich et al.
(1971) prepared a series of Au-Cu alloys as standards for microanalysis with the following chemical composition: Au (80%)-Cu (20%), Au (60%) - Cu (40%), Au (40%) - Cu (60%), Au (20%) - Cu (80%).
So far only 3 species of native Au-Cu minerals have been discovered. Lozhechkin et al. (1939) described a mineral with formula Au2Cu3, named cuproauride. Ramdohr
(1967) described two distinct homogeneous phases: AuCu3 and AuCu.
INSTRUMENTAL
In China, we used electron probe EB-3 (X-ray take-off angle 52.5 ) . The accelerat- ing voltage was 30 KV. Crystal LiF was used to measure CuKa and AuLai and ADP for measuring AgLai.
In England, we used an electron probe designed in the Dept. of Earth Sciences, Cambridge University, by Dr. J.V.P. Long (X-ray take-off angle - 40 ) . This was fitted with a Si(Li),detector and a Harwell type 3073 pulse processor (energy reso- lution "» 156 eV for MnKa) for recording ED spectra. The accelerating voltage was 20 kV. Link Systems ZAF-4 FLS software was used for processing the spectra.
Pure copper, gold and silver metals were used as standards.
RESULTS
We have analysed a number of grains of Au-Cu minerals, which are from a sulphurized copper-nickel deposit in North-West China, sequentially in the Institute of Compre- hensive U t i l i z a t i o n of Mineral Resources, China and in the Department of Earth
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19842147
C2-632 JOURNAL DE PHYSIQUE
According t o t h e chemical c o m p o s i t i o n we c o n s i d e r t h a t Au3Cu2 i s a new m i n e r a l , b u t we have n o t determined i t s space group and u n i t c e l l parameters y e t because o f i t s i n t e r g r o w t h w i t h AuCu, o r AuCu, i t s s m a l l s i z e (about 40 urn) and o n l y two g r a i n s c o n t a i n i n g t h i s m i n e r a l . T h i s new m i n e r a l i s named J i n c h u a n i t e , a f t e r i t s l o c a l i t y . J i n c h u a n i t e i s g r a n u l a r and r e d - p u r p l i s h i n c o l o u r w i t h weak m e t a l l i c l u s t r e , dark- brown r e f l e c t i v e c o l o u r , c l e a r double r e f l e c t i v i t y and s t r o n g a n i s o t r o p y . I t s r e f - l e c t i v i t y i s about 30%, and i t forms i n t e r g r o w t h s w i t h AuCu3 o r AuCu.
Sciences, U n i v e r s i t y o f Cambridge, England, and found 4 species: AuCu, AuCu3, Au3Cu, and n e a r l y pure Au c o n t a i n i n g a few p e r c e n t of Cu. Some o f t h e r e s u l t s a r e g i v e n i n Table 1.
Table 1 Chemical composition o f Au-Cu m i n e r a l s
From Table 1, C228-7 seems t o have f o r m u l a Au2Cu, b u t o n l y a v e r y l i m i t e d a r e a w i t h - i n t h i s g r a i n has such a composition, so we a r e n o t s u r e i f t h e r e i s a c t u a l l y a min- e r a l w i t h formula Au2Cu.
Name o f specimen C81-1-L
~ 8 1 - 1 - ~ C81-1-L
C 228 C 228 C 228 C 228 C 228 C 228 C 1 C24-2 C24-2
Scanning p i c t u r e s o f C81-1-L, C 228, C 1 a r e r e s p e c t i v e l y shown i n F i g u r e 1, F i g u r e 2, F i g u r e 3.
F i g u r e 1. Scanning p i c t u r e s of specimen C81-1-L. (10) AuLal (12) CuKal ( 1 3 ) AgLal (14) Specimen c u r r e n t image
*Analysed i n China i n 1981
O ~ n a l ~ s e d i n Cambridge, U.K., i n 1982 & 1983 s p o t
3*
2 *
4*
7 ~ ' 7 ~ ' 7 ~ ' 11 7:
2O 3 O
8' 1 o0
Chemical composition (%)
Cu Au Ag c
47.95 51.82 0.29 100.06 18.30 81.27 0.33 99.90 17.83 81.98 0.26 100.07 17.79 81.34 0.85 99.98 16.65 82.33 1.02 100.00 18.79 79.98 1.26 100.03 13.15 86.33 0.54 100.02
24.69 75.86
-
100.5524.02 76.35 - 100.37
24.99 75.75 - 100.74
1.95 97.50 - 99.45
2.16 97.18 0.51 99.85
Atomic r a t i o
Cu Au Ag
0.754 0.263 0.003 0.288 0.413 0.003 0.281 0.416 0.002 0.280 G.413 0.008 0.262 0.418 0.009 0.296 0.406 0.012 0.207 0.438 0.005 0.389 0.385 -
0.378 0.387 -
0.393 0.385 -
0.031 0.495 -
0.034 0.493 0.005
I d e a l f o r m u l a AuCU, Au3Cu2 Au3Cu2 Au3Cu2 Au3Cu, Au3Cu2 Au~CU AUCU AuCu AuCu
F i g u r e 2. Scanning p i c t u r e s o f specimen C 228. (a) AuM~I ( b ) CuKa ( c ) AgLal ( d ) Secondary e l e c t r o n image
Figure 3. Scanning p i c t u r e s o f specimen C 1. (a) AuMal ( 6 ) CuKa ( c ) AgLal ( d ) Secondary e l e c t r o n image
JOURNAL DE PHYSIQUE
ACKNOWLEDGEMENTS
We a r e g r a t e f u l t o Dr. J.V.P. Long f o r o f f e r i n g many helpful suggestions, and t o Dr. S. J.B. Reed f o r reading t h e manuscript.
REFERENCES
BARRETT, C.S. & MASSALSKI, T.B., In: S t r u c t u r e of Metals, 3rd Ed. (1966) 270-283.
HANSEN, M. & ANDERKO, K . , In: Constitution of Binary A1 l o y s , 2nd Ed. (1958) 198- 203.
HEINRICH, K.F.J. e t a l . , NBS Special Publication (1971) 260-28, U . S . Government P r i n t i n a O f f i c e , Washington, D.C.
LOZHECHKIN, M.P. e t a l . , Compt. Rend. (Doklady) Acad. S c i . U.R.S.S. s ( 1 9 3 9 ) 451- 454.
RAMDOHR, P . , N. J b . Min. Abh.
