Le, Truong X., Dirks, Paul H.G.M., Sanislav, Ioan V., Huizenga, Jan M., Cocker, Helen A., and Manestar, Grace N. (2021) Geological setting and mineralization characteristics of the Tick Hill Gold Deposit, Mount Isa Inlier, Queensland, Australia. Ore Geology Reviews, 137. 104288.

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Abstract

The high grade (~22.5 g/t), gold-only Tick Hill deposit presents a unique mineralization style in the Mt Isa Inlier. The deposit was mined in the early 1990s, and is hosted in biotite schist, calc-silicate gneiss, quartzite and quartz-feldspar mylonite. These rocks were affected by D1 shearing and D2 upright folding at high-grade metamorphic conditions, followed by D3 events including normal faulting with widespread quartz-feldspar alteration and D4 strike-slip faulting. The Tick Hill ore body was linear in shape and paralleled the D1 mineral elongation lineation, and the intersection lineation between sets of D3 faults. Gold is dominantly hosted within intensely silicified units affected by D3 fracturing and associated alteration. However, some gold grains are contained within syn-D1, peak-metamorphic minerals indicating that mineralization involved two separate events; an early event predating or concomitant with D1 when gold was first introduced and concentrated, and a second event during D3 when gold was remobilized and/or further enriched to be deposited in its final configuration. Mineralization at Tick Hill is characterized by coarse grained gold associated with Bi-selenides, minor sulfides, and a general paucity of other metals except for a slight enrichment of Cu in the footwall to the ore zone. Alteration is characterized by early silicification and magnetite alteration that formed during the initial D1-2 events and may have coincided with the first stage of gold enrichment. During syn-D3 (re-)mobilization of gold, alteration involved the destruction of magnetite, the emplacement of abundant laminar quartz veins, and the deposition of proximal albite, hematite, chlorite, amphibole, epidote overprinted by later K-feldspar, sericite, clay minerals and minor calcite. The ore zone is bounded by a strongly silicified zone and surrounded by a chlorite-epidote shell. The low pressure D3 gold (re-)mobilization event involved an oxidized, S-under-saturated, acidic, saline aqueous fluid. In terms of alteration characteristics, the Tick Hill deposit shares similarities with IOCG deposits in the area. However, its high-grade gold-only nature, lack of Cu, and the presence of Bi-selenides makes it a unique deposit in the Mt Isa Inlier.

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