Abstract

The Paleozoic Scott lode gold-silver epithermal deposit, situated at Pajingo, northeast Queensland, is hosted by feldspathic-volcanolithic sandstones, quartzose sandstones, ignimbrites, andesitic volcanics with interbedded block and ash deposits, lap fill tuffs, and andesitic to dioritic intrusive rocks. The Scott lode deposit contains 1.23 million metric tons of 9.9 g/t gold and 38.9 g/t silver. There are six principal types of alteration assemblages which are zoned with respect to the main vein structure: propylitic, potassic (adularia), intermediate argillic, silicic, kaolinitic, and ferroan carbonate. Over- printing textural relationships indicate that the propylitic type is earliest, progressively followed by potassic (adularia), then intermediate argillic, and finally silicic alteration. Auriferous veins are largely coeval with the silicic and intermediate argillic alteration types. Kaolinite and ferroan carbonate occur as late-stage alteration products, postdating the precious metal mineralization. Principal ore and sulfide minerals include pyrite, sphalerite, galena, chalcopyrite, hessite, tennantite-tetrahedrite, argentite, petzite, electrum, and native gold. Gangue minerals in the veins are quartz, illite, adularia, calcite, and locally, kaolinite. The main-stage quartz is zoned with respect to mineralogy, mineralization styles, metal distribution patterns, and vein textures. Three major zones can be recognized: zone I--an upper precious metal, moss chalcedonic crustiform-colloform quartz zone, zone II--intermediate precious + base metal, crystalline quartz-coarse-grained sulfide-dominated, crustiform-colloform quartz zone, and zone III-- deep sparse base metal, weakly banded crystalline comb quartz zone. The ore interval occurs in zones I and II with the transition to zone III effectively defining the limit of mineralization. Economic mineralization at the Scott lode deposit was laid down from dilute fluids (0.7-2.5 wt % NaCl...

First Page Preview

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