GSA SGEG Facets of Exploration - Sarah Jones presents Structural geology for ore deposit exploration

Sarah's Biography: After 3.5 years working for Gold Fields Ltd as their Chief Structural Geologist, Sarah Jones is currently living back in NZ and working in her own structural geology consultancy (SJGeology Ltd). She has over 20 years of extensive field mapping experience within Australia and overseas. Sarah has worked as a structural geologist for the last 12 years on numerous deposits and deposit styles. Prior to Gold Fields, she was based in Kalgoorlie as a regional mapper with GSWA for about 5 years after completing a PhD at CODES at the end of 2001. The PhD study was on a VMS deposit (Myra Falls) in Canada. She worked in the Eastern Goldfields at Darlot Gold Mine as an exploration geologist for a few years after completing her BSc and MSc at Otago University, New Zealand. Her Masters project was based on a mapping study in South Victoria Land, Antarctica. In 2018, Sarah received the AB Edwards medal from the Geological Society of Australia's Specialist Group for Economic Geology.
Talk Abstract: Successful exploration for any type of ore deposit requires a good understanding of the formation and likely setting of the targeted ore body. To understand a mineralised system, we need to know the nature of the host rocks (their age, composition, geological setting), the nature of the host structures, and relative timing of mineralisation vs the local/regional deformation history. This information can then guide us to the most likely type of orebody present in the target area.
Commodities like copper or manganese occur in numerous geological settings and it is important to understand the different modes of formation. For example, manganese is found in large stratabound sedimentary deposits or in smaller high-grade fault-hosted hydrothermal deposits. Structural geology is a key component for understanding the geological setting and mode of ore formation.
Structural geology is also key to determining the setting and timing of gold deposits. In the Eastern Goldfields, WA, recent work has shown that although many deposits are associated with horizontal east-west compression (D2-3 event; orogenic gold), others have formed during an earlier D1 event (granite-up, greenstone-down tectonics). The setting and structural controls on ore formation on these older deposits differs markedly from the more typical D2-3 orogenic gold deposits.
This presentation examines two exploration case studies: manganese deposits in the Pilbara, and gold deposits in the Agnew district, Eastern Goldfields. Successful exploration requires an open mind on deposit types and possible ore formation, regardless of the commodity.