Sulphide mineralisation in the Olary Block, South Australia

Abstract

The South Australian portion of the Willyama Inliers hosts a diversity of small sulphide and uranium deposits and numerous outcropping gossans. This fact, together with geological similarities to the adjacent Broken Hill Block has led to extensive exploration. A broad classification distinguishes two main types of sulphide mineralisation: 1) stratiform iron sulphide-dominated (+Cu, Zn, Co) deposits which occur widespread within specific stratigraphic intervals, and stratabound occurrences of syn-depositional to diagenetic origin which show some structural control; 2) syn-tectonic to post-peak metamorphic replacement and vein-type deposits (Fe-Cu-Au and Cu-Zn-Pb), which are hosted by fractures and within faults and shear zones. These occurrences show no stratigraphic control and are not spatially related to type 1 mineralisation. Late-stage deposits also differ from stratiform/stratabound mineralisation in their texture, mineral assemblage and geochemical composition. Much of the sulphide mineralisation in the Olary Block has been interpreted as resulting from rift-associated syn-to diagenetic processes, such as hot spring exhalations and base metal precipitation along reduction-oxidation interfaces. Subsequent granitic intrusive, high grade metamorphic and multiphase deformation events would have induced remobilisation and redeposition of sulphides in a variety of epigenetic modes. However, a detailed petrographic and geochemical study of sulphide mineralisation in the Olary Block demonstrates that due to the lack of abundant pervasive fluids, translocation and modification of preexisting sulphides were restricted to less than a few centimetres. Instead, widespread syn-tectonic to epigenetic (i.e., post-peak metamorphic) mobilisation of ore constituents occurred to form retrograde sulphide mineralisation as well as multiple generations of late-stage vein deposits. These epigenetic deposits are genetically unrelated to synsedimentary and diagenetic occurrences, an aspect of significance for exploration in the Olary Block. Temporal separation of peak metamorphism in deeper crustal levels from its occurrence in shallow levels, periodic tectonic disturbances and repeated seismic pumping are processes believed to have resulted in intermittent mobilisation of ore constituents from a deep-seated metasedimentary reservoir.

Iron oxide copper-gold (IOCG) deposits – A review (part 1): Settings, mineralogy, ore geochemistry and classification

“…This style of mineralisation, which lacks significant Fe-oxides, has been likened to 'redbed' or stratiform sedimentary Cu (-Co) deposits such as those in the Zambian copper belt and the Kupferschiefer in Europe (Cook & Ashley, 1992). Among the wide range of epigenetic sulfide deposits and occurrences in the Olary Domain (Bierlein et al, 1995) the White Dam Au (-Mo) deposit is distinctive in its lack of iron oxides, syn-deformational quartz-Kfeldspar-plagioclase-biotite vein style, high Au:Cu ratio, and lower stratigraphic position within medium grade metamorphic host rocks, compared to the main Cu-Au-Mo deposits . Molybdenite has yielded Re-Os ages of ~1631 Ma, ~1616 Ma and ~1612 Ma for the White Dam deposit (Fig.…”

Geology and mineralization characteristics of Khamkeut Saen Oudom gold deposit, Bolikhamxai, Lao PDR

“…Tongyoung (Yoo et al, 2010) and Cheongyang (Yoo et al, 2006) are mesothermal deposits have similar range to KSO. Orogenic gold deposit from Olary block in South Australia (Bierlein et al, 1995) and Yuryang deposit in Korea (Pak et al, 2005) also shown similar to KSO (Fig. 5.6).…”

“…FeS mole % in sphalerite of other deposits; for example, Pongkor in Indonesia (Warmada et al, 2003) has value 0.1 to 2.0 mole %, Central Khamchatka in Russia (Andreeva et al, 2013) has value around 0.0 to 3.0 mole %, Tongyoung in Korea (Yoo et al, 2010) has 6.2 to 13.8 mole %, Cheongyang in Korea (Yoo et al, 2006) has 5.9 to 8.3 mole %, Yuryang deposit in Korea (Pak et al, 2005) has 11.0 to 17.6 mole %, Olary block in South Australia (Bierlein et al, 1995) has 3.8 to 18.7 mole %.…”