Gold deposits

The Drake Ag-Au deposits in northern New South Wales occur in Permo-Carboniferous volcanic rocks mineralisation is considered to result from hydrothermal activity associated with the acid volcanism (Bottomer, 1986). At one of these deposits. Lady Hampton, stratabound mineralisation occurs as disseminations in a volcaniclastic unit exhibiting sericite-clay-quartz alteration. Pyrite is the major sulphide present with minor sphalerite, galena, chalcopyrite, Ag sulphosalts, tennantite and native alloys. 

Aftabi and Azzaria (1983) studied the distribution of Hg in ore and host rocks from the Sigma Au Mine, Val D Or, Quebec. The deposit occurs in deformed Archaean metavolcanic rocks of ultrabasic and tholeiitic composition which are intmded by diorite porphyries and undeformed porphyry dykes. Gold mineralisation occurs in sub-vertical and sub-horizontal veins associated with chloritisation, silicification, albitisation, sericitisation and minor carbonatisation. Background Hg contents in the metavolcanic host rocks averaged about 5 ppb compared with 80 ppb in ore veins and rocks associated with ore. However, the distribution of Hg was found not to be wider than that of Au, Ag, As, Zn or Cu in the various host rocks (Fig. 12-6). 

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In the Commonwealth of Independent States (CIS, formerly the USSR), nearly 50% of the CIS production comes from Ka2akhstan. Silver is produced from the lead—2inc mines at Ostkamen, Shymkent, and Leninogorsk (ca 1000 t) and also in Russia s Far East, where it is a by-product of the tin deposits near Khabarovsk, and of the copper and gold deposits in the Ural Mountains. 

The hardness of such coatings may reach a maximum of about 400 Hy as compared with approximately 50 Hy for a soft gold deposit. A series of corrosion studies in industrial and marine atmospheres by Baker" has indicated that the protective value of hard gold coatings is comparable with that of the pure metal, and that a thickness of only 0-002 5 mm gives good protection to copper base alloys during exposure for six months. 

Clarke s study of the porosity of gold deposits lasted for a decade . Reviewing the topic, Garte concluded that, to reduce porosity (1) the substrate surface should be smoothed chemically or electrochemically (2) certain undercoats are beneficial and (3) plating conditions must be tightly controlled . Better procedures led to a reduction of thickness requirements—e.g. from 5 to2-5 /im on connectors, provided other requirements are satisfied. 

Gold plating and other methods of gold deposition... 

This, like Example, is an electrochemical stoichiomehy problem. It asks about the amount of gold deposited in an electrolytic reaction. The method is the same as that of Example. ... 

Figure 4. Particle size histograms for the gold deposited onto various carbon samples. (Partially reprinted from Topics in Catalysis, 122 (1) 2007, pg 248, with permission from Elsevier Science).

Figure 1.6. Di.stribution and temporal and spatial relationship of late Cenozoic gold deposits in the Japanese Islands. 1 Quartz vein-type gold deposits with little to no base metals. 2 Gold-silver deposits with abundant base metals. 3 Distribution boundary of gold deposits formed during the Miocene. 4 Location of Plio-Pleistocene gold deposits at the actual island arc junctions. 5 Location of Plio-Pleistocene gold deposits in front of the actual island arc junctions. Numbers in the figure are K-Ar ages of epithermal Au-Ag veins (Kubota, 1994).

Recently, epithermal gold deposits were divided into several types based on gangue minerals, and physicochemical environment of ore deposition (pH, H2S concentration of ore fluids). They are hot spring-type (Silberman, 1982 Berger, 1983a Berger and Eimon,... 

Tonnages of gold, silver and the other associated metal, silver/gold ratio, K-Ar ages and host rocks for the Te-type and Se-type epithermal gold deposits (Shikazono et al., 1990)... 

Figure 1.117. Map showing the distribution of Se-type and Te-type epithermal gold deposits in Japan. 1 Green-tuff and subaerial volcanic region of Tertiary/Quaternary ages, 2 Main Paleozoic/Mesozoic terrane, 3 Main metamorphic terrane, 4 Te-type deposits, 5 Se-type deposits, 6 Te- and Se-bearing deposits, ISTL Itoigawa-Shizuoka tectonic line, TTL Tanakura tectonic line, MTL Median tectonic line (Shikazono et al.,I990).

Figure 1.133. The normal order in other epithermal gold deposits in Japan (Nagayama, 1993a).

This reaction suggests that oxidation of fluids is important as a depositional mechanism. However, this oxidation reaction seems difficult to explain the gold deposition from the following reasons. 

The rate of oxidation of H2S to is slow at a site of gold deposition. 

This reaction proceeds due to the degassing of H2, decreasing of H+ and probably decreasing of temperature. We cannot evaluate this reaction as an important cause for gold deposition because no study on this reaction has been done. 

Reed and Spycher (1985) made a computation on the gold deposition from the mixed fluids. Their results support that gold deposition occurred in the Hishikari veins... 

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