Summary:
The Chatree deposit and SE Complex is located between Phichit and Phetchabun Provinces, central Thailand, and is hosted by Late Permian to Early Triassic volcaniclastic and volcanogenic sedimentary rocks.
The Chatree Gold Mine is a low sulphidation epithermal gold–silver deposit located in the Loei – Phetchabun volcanic belt in central Thailand. The deposit spans 2.5 by 7.5km and consists of 8 vein zones, five of which have been mined by open-pit methods.
The Chatree low sulphidation epithermal gold–silver deposit occurs as veins, stockworks and minor breccias hosted by a volcanic and volcanogenic sedimentary facies. The main gold–silver mineralisation is characterised by colloform–crustiform banded quartz ± carbonate ± chlorite ± adularia–sulphide– electrum veins. Gold mainly occurs as electrum, both as free grains associated with quartz, carbonate minerals and chlorite, and as inclusions in sulphides, mostly pyrite (Salam et al., 2013).
Oxidation and broad stratigraphic units control the gross distribution of gold and silver mineralisation with specific geological units providing preferred mineralisation hosts. These are most notable at the A Pit where the sedimentary unit hosts the majority of mineralisation. At a local scale, mineralisation is controlled by structures that cross-cut lithological trends. A knowledge of local litho-structural mineralisation controls was utilised when estimating resources. Barren post-mineralisation dykes with widths varying from less than one to around eight metres cross-cut mineralisation.
In the mine area, the host volcanic sequence comprises four main units. The basal unit is dominated by andesite lavas and breccias, containing dacite dome complexes. This is followed by a thick sequence dominated by andesitic breccia. Overlying this is a largely sedimentary package with interfingering rhyolitic breccias. The uppermost unit in the mine area is a lithic rich fiamme breccia. As the lithologies interfinger, the locations of some unit boundaries in core, and especially in chips, are not always clear. All units are cut by dykes, predominantly andesitic, and typically less than 10 metres wide.
Mineralisation
Epithermal gold deposits, such as those at Chatree, are generally formed in areas of active volcanism around the margins of continents, and may be associated with “bonanza” or high grade style mineralisation. Mineralisation in such deposits is deposited from hot fluids which are estimated to range in temperatures from less than 100 degrees centigrade to approximately 300 degrees centigrade. The mineralisation contained in these fluids is deposited as they rise to elevated crustal settings and boil, cool or mix with evolved nearsurface waters which oxidise the fluids to promote high grade gold deposition. The fluids usually travel toward the surface via fractures in the rocks and the resulting mineralisation often occurs at the intersection of these fractures and brittle host rocks in layered volcanic sequences.
The gold mineralisation is closely associated with a variety of types of quartz carbonate veins, some of which contain sulphides. They vary in width from millimetres to tens of metres. Significant amounts of silver and very minor amounts of zinc and lead are also associated with the mineralisation. The deposit is classed as low sulphidation epithermal, and sulphides tend to comprise less than 3% of the ore mass (Cumming, et al). Visible gold is rare within the system. Chlorite is common both in the veins and as alteration in the host rock.
The style of quartz carbonate gold mineralisation found at Chatree is common to a number of the most prolific gold producers in the Pacific rim, including Porgera and Misima in Papua New Guinea, Kelian and Mount Muro in Indonesia (Corbett). The variety of low sulphidation epithermal gold deposits all display controls dominated by structure, competent host rocks and efficient mechanisms of Au deposition.
The largest prospect in terms of the currently defined mineral resource is A Prospect. Here, the sedimentary unit in the middle of the package of volcanics appears to have acted as a favourable rock unit for mineralisation, with the overlying fiamme breccia acting as a lithological trap to fluid movement, due to low permeability and/or competence contrast. The stockworks and sheeted quartz veins which host gold mineralisation are mainly vertical to steeply west dipping and are best developed in the sedimentary unit which itself dips at 20o to the east. Veining outside this unit tends to be sparser in density, but may still contain gold.
At Q Prospect, in the most northern section of the mining leases, the mineralisation is characterised by brecciation of the host silicified sediments, and has been interpreted as including both strata bound and sub-vertical feeder like zones.
In the southern leases, mineralisation tends to be in fewer discrete veins, with fewer stockworks, and in the C and H Pits area the veins dip northwest at 30 to 70.
Dimensions
The approximately N-S strike length of the portion of the Mineral Resource that was updated around the A Pit area is ~2,000m. The E-W width is ~1,200m and the depth below surface is ~600m.
Chatree South-East Complex (CSEC)
The SE Complex is a south-eastern extension of the Chatree orebody.
The area is divided into six zones including Main, Western, Northern, Northeastern and Southern zones and T Prospect. CSEC is interpreted as a peripheral component of the Chatree epithermal system. The main lithological units are: fiamme breccia, volcanogenic sediments, rhyolitic tuff, andesitic tuff and basal andesite. These units have been intruded by andesite, porphyritic andesite and feldspar porphyry dykes.
Gold mineralisation is found mainly within volcanogenic sediments and polymictic rhyolitic breccia and is associated with quartz-carbonate veins, containing 3–10% sulphide (mainly pyrite) in the form of clots, dissemination, and fracture fill. Supergene enrichment occurs in some areas up to 20m below surface.
Main And Western Zones
Gold mineralisation is associated with silicified and phyllic-altered sedimentary rocks and rhyolitic breccias with some quartz veins and disseminated pyrite. Mineralisation at the main zone is trending NNW and shallow dipping (20 degrees) to the east, where fine-grained sediments are thicker and more fractured, either due to facies change and/or structural repetition (similar to Unit two at Chatree Gold Mine). The western boundary of mineralisation is relatively well defined and suggests that a controlling structure, such as a reverse fault, may be present at the base of mineralisation.
Northern Zone
Mineralisation is mainly associated with phyllicaltered and silicified rhyolitic tuff and polymictic rhyolitic breccia, containing 1–5% quartz veins and 1–10% disseminated pyrite.
Northeastern zone
Drilling focused on infill lines to establish the continuity of gold mineralisation zones that were identified in 2024 and has confirmed that mineralisation extends from the Main zone toward the Northeast for >500m. Gold mineralisation is mainly hosted within silicified/ phyllic altered polymictic rhyolitic breccia, rhyolitic tuff and sediments, containing trace to 10% quartz veins and 2–10% fine-grained disseminated pyrite.
Southern zone
Drilling results confirmed that gold mineralisation is generally associated with a silicified sedimentary unit, comprised of pale to dark grey siltstone and sedimentary breccia with small quartz stockwork veins and 5–10% disseminated pyrite.
T prospect
Geology is predominantly andesitic (polymictic) tuff with locally intercalated rhyolitic tuff. Gold mineralisation is related to a sub-vertical zone of quartz veining, containing 3–5% pyrite within zones of phyllic-altered and silicified host rock.
Mineralisation extends from Chatree Mine D pit in a south-west direction.