Abstract

Mercury in the Woodlawn (New South Wales, Australia) Zn-Pb-Cu volcanogenic massive sulfide deposit is concentrated in the northern part of the deposit, away from the central volcanic pile source area. The mercury content of the massive sulfide ore ranges from less than 100 ppb to 18,000 ppb in tetrahedrite-bearing ore, with a median mercury content of 3,600 ppb. Programmed heating determinations show mercury to occur in some of the sphalerite with, locally, large amounts present in tetrahedrite. The mercury content of sphalerite ranges from 650 to 21,000 ppb, chalcopyrite from 220 to 3,700 ppb, galena from 220 to 2,100 ppb, and pyrite from less than 10 to 4,600 ppb, with the highest levels occurring near the hanging wall. Throughout the ore zone, mercury does not significantly correlate with the Zn, Pb, or Cu content of the ore, but there is very significant correlation with the Ag, As, and Sb content.The supergene ore is a zone of mercury depletion with mercury ranging from 150 to 1,700 ppb, and there is a significant correlation of mercury with Ag, As, and Sb.The lower part of the oxidized ore profile is a zone of mercury enrichment in which mercury ranges from 270 to 39,000 ppb. The mercury content correlates very significantly with Ag, As, and Sb content and programmed heating determinations show mercury to be present in complex sulfate and arensate minerals, such as beudantite and plumbojarosite. Cerussite also contains appreciable mercury.The upper part of the oxidized ore profile and gossans contain low mercury levels, ranging from 10 to 710 ppb. The lack of correlation of mercury with the Ag, As, and Sb content in the oxide mineral-dominated zones suggests mercury to be mobilized from within these zones. The extent and magnitude of mercury dispersion halos over oxidizing sulfides may be governed by the size and stability of the oxidized zone.Mercury dispersion in the soil is fairly narrowly confined to the ore suboutcrop in thin skeletal soils, but in soils with better developed profiles, dispersion of mercury is more extensive. Mercury in soil gas was measured at 8 ng/hour over the northern part of the ore zone but was not detected over the southern end.There is no primary dispersion halo of mercury in the extensive zones of hydrothermal alteration around the massive sulfide ore. Mercury in wall rocks is held predominantly in disseminated and stringer sphalerite and pyrite mineralizations, which are recognized in ore horizon-equivalent rocks for over 500 m south of the ore zone.

First Page Preview

First page PDF preview
You do not currently have access to this article.