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Home , Vein (geology)

0393-000103 Key Structural Components to Orogenic Sedimentary Hosted Vein (SHV) Deposits

Corresponding author: Paul D Klipfel, Resource Services Inc, [email protected]

Orogenic gold deposits include a diverse range of deposit sub-types. Gold deposits historically known as shale-hosted, turbidite-hosted, or mesothermal vein deposits in sedimentary host rocks, can be grouped into the Hosted Vein (SHV) family of deposits which are united by a set of common characteristics. These include thick sedimentary sequences (>5 km) of Neoproterozoic to early Paleozoic passive-margin interlayered shale-siltstone host rocks; extended crust as basement substrate for the host sedimentary assemblage; multiple episodes of deformation of which -thrust- orogenesis is the most significant; Au±As, Sb, W metal suite; neutral, low to moderate salinity hydrothermal fluid chemistry; minimal to moderate grade metamorphism; active plutonic magmatism at or near the time of mineralization; numerous, widespread regional gold occurrences; and spatially associated significant gold placer deposits.

SHV deposits are most common in deformed rocks along the paleo-Tethyan margin of Asia. The most prominent examples include Murunatu, Sukoy Log, Baleyskoe, Maysky and Kumtor in Asia along with gold vein deposits of the Victorian Goldfields in Australia. Similar settings elsewhere in the world also host SHV deposits and include those of the Otago Schist Belt, New Zealand, the Meguma of Nova Scotia, Nome, Alaska, Puna region of Argentina and Bolivia, as well as the western margin of Canadian North America.

Orogenesis is essential but not sufficient for the formation of these deposits. Significant crustal shortening with moderate to significant thickening appears to be a necessary condition. SHV deposits are not known to have formed during orogenic events where there is apparent inadequate crustal thickening. Two other structural features also appear to be fundamental to SHV host . First, extension faults formed during continental breakup create broken, unstable crust as basement for . These primary, destabilizing structures propagate upward through the passive margin sedimentary sequence during deposition and . Later they provide key crustal-scale connectivity for fluid focusing and migration upward along deeply- rooted to upper mid-crustal pathways over broad regional extents. Second, virtually all significant SHV deposits occur in proximity to mapable or inferred crustal scale structures and/or in association with specific fluid traps. Absence of quality traps produces regional dispersion of gold among countless veins, but limited opportunity for sizeable economic concentrations of gold. Other structural components that may be important in some cases but are not essential include primary soft-sediment and slope-failure structures as well as late to post orogenic tectonic events, particularly .

The spatial association of granitic plutonism is common to many SHV regional settings. However, the timing of magmatism can be pre-, syn-, or post-mineralization and no clear, consistent linkages have been established between plutonism and mineralization. It is suggested that orogenesis produces both hydrothermal fluid and magma with the former able to migrate upward through the crust more rapidly than more viscous magma. The opportunity is present for contribution of magmatic fluids and metal to crustal dewatering fluids through mixing and co-mingling during upward migration through the crust as is abundant opportunity for fluid and wall interaction.