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).

Sepon mine is an open pit operation that is mining and processing supergene copper ore. The operation uses a fleet of excavators and articulated trucks along with a fleet of auxiliary equipment. This mining method is appropriate for the style and size of the mineralisation.

Pit optimisations and designs adhered to recommended geotechnical parameters. The inter-ramp slopes used range between 18° – 40° for the clay material and 35° – 50° for the more competent material.


Underground Exploration

With a mineral resource of 9.5 million tonnes and projected ore production to increase from 400,000 tonnes in 2023 to 1.2 million tonnes per annum thereafter, the “Discovery Deeps Underground Mine” is expected to extend Sepon’s mine life for at least another seven years, to 2030, contributing to poverty reduction and sustainable development in host communities.

The underground mine will extend 450 metres below the surface. The decline access tunnel will be more than 1,800m long, 5m high and 5m wide to accommodate modern underground excavation and drilling equipment.

The Sepon mine is an operating entity. The metallurgical process is a hydrometallurgical process involving grinding, tank leaching, autoclave leaching, solvent extraction and electrowinning.

The Sepon copper operation produces approximately 80,000 tonnes of copper cathode (copper sheets) per year from the nearby Khanong and Thengkham ore bodies.

Processing methods:
Gold - Flotation, POX and Carbon-in-leach;
Copper - Whole-of-ore leach, solvent extraction and electrowinning.

SEPON 2.5 is a project to increase design throughput capacity of primary ore through our processing plant from the initial 1.5Mtpa to 2.5Mtpa. We will introduce an additional mill ball, oxygen facility, POX, flotation, and new steps in leaching and the CCD circuit.

Gold production ceased in 2013 and resumed in June 2020.

Crushing and milling
Run-of-mine (ROM) ore is crushed and then milled, which reduces the diameter of the pieces of rock from abo ........