North Silver Bell, Arizona

The most abundant sulphur gases determined at North Silver Bell were CSj and COS  

18 of the 30 samples contained CSi, with the highest concentrations located over the ore body (Fig. 8-25) 15 samples contained COS, with the highest concentrations located over the alteration zones around the ore body (Fig. 8-26). Only four of the 30 samples contained measurable HjS, one over the ore body and three over the alteration zones. 

Although SO2 was not expected, because of its high solubility in water, nine of the 30 samples, located mostly over the ore body, contained 300-1000 ppb SO2 (Fig. 8-27). The occurrence of SO2 may be attributed to the hot, dry enviroiunent at North Silver Bell, and to the shallowness of the deposit, which permitted some of the SO2 from oxidising ore to reach the surface before it dissolved in moisture within the leached capping and overlying alluvium. 

EXPLANA1ION Propylytic alteration Phyltic alteration Potassic alteration Sample site 

Carbon disulfide in head-space gas Range not detected at lower limit of detection (50 ppbMOOO ppb 

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Fig. 8-25. Geology, mineralisation, soil sample sites and CS2 concentrations at North Silver Bell, Arizona (from Hinkle and Dilbert, 1984).

Lopez, J.A. Titley, S.R. 1995. Outcrop and Capping Characteristics of the Supergene Sulfide Enrichment at North Silver Bell, Pima County, Arizona. In Pierce, W. Bolm, J.G. (eds.). Porphyry copper deposits of the American Cordillera Arizona Geological Society Digest, 20, 424-435. 

Butt, C.R.M., Hart, M.K.W. and Gole, M.J., 1985. Gases and trace elements in soils at the North Silver Bell Deposit, Pima County, Arizona Discussion. J. Geochem. Explor., 24 129-134. 

Graybeal, F.T. 1982. Geology of the El Tiro area Silver Bell mining district, Pima County, Arizona. Advances in Geology of the Porphyry Copper Deposits Southwest North America. University of Arizona Press, Tucson, AZ. 

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