Undergraduate Honors Theses

Thesis Defended

Spring 2016

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Geological Sciences

First Advisor

Charles Stern

Second Advisor

Lang Farmer

Third Advisor

Sheralee Brindell

Abstract

Browns Creek is a skarn that hosts an Au-Cu ore deposit in the Blayney region of New South Wales, Australia. Skarn rock at this location is wollastonite marble, highly mineralized by sulfides and gold deposited as native Au, electrum, telluride minerals and within arsenopyrite crystals. Related alteration includes metasomatized hornfels of the Ordovician Blayney Volcanics and marbleized interbedded limestone lenses of the Cowriga Limestone Member. Magmatic fluids responsible for this alteration were derived from a Silurian felsic-intermediate multi-phase intrusive system, the Browns Creek Intrusive Complex. Main constituents of this intrusive system include the Carcaor Granodiorite, the first and largest phase responsible for main pluton emplacement and skarnification of country rock, and the Mine Dyke Group, which is a smaller and more felsic phase attributed to carrying the ore-bearing fluids deposited at Browns Creek.

As a small mine that is no longer operational, Browns Creek offers an example of an economic deposit that has not been thoroughly studied. This honors thesis aims to use petrological and geochemical analyses to better understand the conditions associated with gold deposition at Browns Creek by focusing on host rocks and metallic minerals deposited outside of the primary ore zone. polished blocks and thin sections were prepared for petrographic and microprobe analysis in order to more fully comprehend mineralogical processes occurring here, and supporting evidence was found for striking results presented by the most recent study on this site. These results include the assignment of Browns Creek as a skarn-hosted ore deposit resulting from a magmatic event post-alteration rather than a true skarn deposit, in addition to the re-dating of Browns Creek Intrusive Complex—presenting a Silurian age ~15Ma older than previously understood. These notable distinctions are investigated here through different approaches than previously explored. Additionally, links are proposed between Browns Creek deposit characteristics and tectonic regime, assigning primary Au-Cu ore deposition to a Silurian volcanic arc environment while suggesting that anomalously occurring Sn mineralization is the result of a later Devonian event within a rifting environment.

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