A Solubility Model for Deposition of Stratiform Massive Sulphide Deposits, New Brunswick, and its Relation to the Distribution of Gold and Palladium

Abstract

<p>Gold and palladium concentrations have been determined in sulphide ores and host rocks of the Caribou, Brunswick No. 12 and Heath Steele mines, New Brunswick, by neutron activation analysis. Gold contents vary from 100 to 6000 ppb in the ores. Gold correlates positively with lead and zinc in the Caribou and Brunswick No. 12 deposits, but is uncorrelated with base metals in the Heath Steele B -1 orebody. Palladium contents range from 3 to 0.1 ppb and, in contrast with gold, show no correlation with base metals in any of the mines. Thus, transport and depositional processes controlling palladium distribution remain obscure. An analysis of the variation of gold content of separated minerals found in replicated analyses, suggests that the dominant mode of occurrence is the native metal.</p> <p>Based on work by Sato (1972b, 1973), a comparison with the Kuroko deposits and analytical data collected by the author, a syngenetic model for metal distribution in the New Brunswick ores has been developed. On the basis of such features as shape, lamination, initial grain size and metal ratios, it is suggested that these latter ores were formed at lower temperatures and from solutions of higher density than the Kuroko deposits.</p> <p>The correlation of gold with lead and zinc is similar to that found in the Kuroko and is inexplicable in terms of chlorocomplexing (Helgeson, 1969) for either Kuroko or New Brunswick stratiform deposits. It is concluded that gold sulphide complexes are the most likely species responsible for gold solubility and transport in the ore solutions which formed these deposits.</p> <p>The zoning of gold from low concentrations in copper-rich ore to higher concentrations in lead-zinc ore is thought to reflect gradual saturation of an ore solution with respect to gold in the waning states of sulphide precipitation. Decreasing temperature, fugacity of oxygen and molality of aqueous sulphide, together with increasing ore solution pH, are primarily responsible for attainment of saturation with respect to metallic gold.</p>