Abstract

The Heath Steele mine is located 35 mi. NW. of Newcastle, New Brunswick, Canada, Middle Ordovician Tetagouche group rocks, consisting of siliceous and basic volcanic rocks and fine-grained quartz sericite schists and porphyry, have been folded into a steeply plunging recumbent anticline. The ore deposits of Zn, Pb, and Cu are associated with minor folding and or sheared dilatent zones at or near the contact between porphyry and fine grained sericitic schist. Mineralogically the sulfide bodies consist of early, euhedral arsenopyrite, magnetite, and pyrite, followed by interstitial pyrrhotite, sphalerite, chalcopyrite, and galena. Minor minerals are tennantite-tetrahedrite, bismuthinite, marcasite, hematite, and some graphite. Supergene minerals consist of chalcocite, covellite, and marcasite with a little native Ag. Little hypogene replacement has taken place between the minerals, which show a "porphyritic" texture. S isotope ratios have been determined for over 150 sulfide and sulfate specimens from 5 of the 7 ore bodies, and from granite, acid and basic volcanics porphyry, and sediments. The results indicate that there is no detectable fractionation either during hypogene mineralization or supergene enrichment. The spread (21.82-22.02) covered by the ratios is narrow, and suggestive of a well homogenized source of mineral solutions. The enrichment of S 34 in the ore sulfides and the presence of graphite, evident from mineralographic studies and mass spectrometric analysis, suggests reduction of original sulfates (known to be enriched in S 34 ) by organic C at temperatures in excess of 600 degrees C. A calculation based on the isotopic exchange reaction between sulfide and sulfate under equilibrium conditions and the spread of the ratios indicates a temperature of 700-800 degrees C. for the source. Finally the ratios determined for sulfides in a gneissic granite close to Heath Steele have the same ratio as the ore. These factors are considered to be diagnostic of a magmatic hydrothermal origin for the ore deposits. In conclusion the writer believes that an origin source bed has been buried until suitable temperatures were reached to cause granitization, reduction of sulfates, and mobilization of the resulting sulfides to form ore deposits at favorable loci.

First Page Preview

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