Summary:
The Sepon project area is situated near the eastern margin of the intra-continental Khorat Basin and on the western flank of the Anamite Range fold belt. It lies within the Troungson geological region covering a broad spectrum of rocks ranging in age from Upper Proterozoic to Jurassic. The regional geology is dominated by an Upper Palaeozoic sedimentary belt of arkosic and feldspathic sandstone, variably calcareous and carbonaceous siltstone, shale and limestone which is variably dolomitised and locally marble. There are lesser volcanic rocks, typically comprised of agglomerate, conglomerate, tuffaceous sandstone, and rare coherent volcanics. The belt is cut by plutonic to sub-volcanic bodies of granite, monzodiorite, granodiorite, quartz porphyry, rhyodacite porphyry (RDP) and andesite porphyry. The intrusive rocks are preferentially emplaced along either east or north-west trending well-developed structures.
Several styles of mineralisation have been recognised within the Sepon Mineral District: porphyry-like Cu-Mo-Au mineralisation, skarnoid Cu-Mo-Au mineralisation adjacent to porphyry intrusive, distal skarn related Cu-Au-Ag+/- Pb+/-Zn massive sulphide veins, Carlin type carbonate hosted gold mineralisation and carbonate hosted Mississippi Valley type Pb-Zn-Ag mineralisation. In addition weathering and supergene re-mobilisation has created supergene copper, exotic supergene copper, oxide gold and alluvial gold in karst fill deposits.
All primary deposits are hydrothermal and, at least spatially, related to the RDP intrusive. Supergene copper mineralisation results from the oxidation, dissolution and transport of primary sulphide hosted copper mineralisation to sites where chemical conditions result in copper precipitation (reduced groundwater, replacement of sulphide, reaction with alkali carbonate). Supergene copper mineralisation occurs above and down slope of primary mineralisation. Chalcocite mineralisation replaces massive pyrite immediately above the skarns. Copper carbonate mineralisation occurs where copper rich groundwater reacts with carbonate rocks. The best supergene copper zones occur above higher grade zones of primary mineralisation and have a vertical profile with the best grades immediately above the base of weathering.
Primary gold mineralisation occurs as Carlin style gold forming distally to the copper skarn systems. Mineralisation occurs in association with decalcification and partial silica replacement of calcareous mudstones (‘jasperoid’) along steep faults, and is typically best developed at the contact of the Nalou Formation (dolomite) and the overlying Discovery Formation (nodular calc-shale).
Dimensions
Sepon hosts a number of deposits, the dimension of each deposit included in this Mineral Resource are listed below:
- Thengkham Ridge (combined Thengkham North, South and East, TKS, TKE and Songkham West) 15000mE-22900mE, 72800mN-75656mN, 0mRL-600mRL;
- Phabing: 15950mE-17750mE, 74250mN-75470mN, 0mRL-500mRL;
- Khanong: 26600mE-29125mE, 74748mN-76524mN, -50mRL-650mRL;
- Discovery West: 23875mE-25555mE, 75250mN-75970mN, 0mRL-300mRL;
- Discovery Main: 25500mE-28200mE, 75250mN-77110mN, 150mRL-450mRL;
- Nalou: 22700mE-24500mE, 73730mN-75350mN, 150mRL-325mRL;
- Namkok West: 24500mE-26060mE, 74000mN-75320mN, 0mRL-300mRL;
- Phavat North - Dankoy: 15300mE-17460mE, 73700mN-75200mN, -0mRL-650mRL;
- Vang Yang South: 27100mE-27820mE, 72400mN-73300mN, -0mRL-500mRL;
- Houay Bang: 33200mE-33992mE, 76500mN-77304mN, 50mRL-450mRL;
- Muang Luang: 25500mE-26250mE, 76700mN-7752mN, -330mRL-350mRL.