The Khao Soon Tungsten Project is located approximately 600km south of Bangkok in Nakhon Si Thammarat Province, Southern Thailand.
The Khao Soon deposit was discovered by Siam American Mining Enterprise Co., Ltd in October 1970 (Shawe, 1984). After discovery but before a concession was granted by the government, the area was ‘rushed’ and illegal mining commenced with an estimated 30,000 people working the field.
The Khao Soon deposit was a major underground tungsten mine which operated for about 10 years up to 1979/80. The US Bureau of Mines Mineral Yearbooks (1971-1980) provides annual recorded tungsten production for Thailand and several cursory references to Khao Soon during the 1970’s including that, in some years Khao Soon was responsible for half or much of all tungsten production and 75% of wolframite production in Thailand. During the period 1971-1980 recorded tungsten concentrate production in Thailand was around 44,000 tonnes. Actual production would have been greater. Therefore, it seems reasonable that estimated concentrate production from Khao Soon was somewhere between 10,000-20,000t for the period 1971-1980. Local sources also indicate that small scale mining continued into the early 1980’s.
Throughout the old mine area there are extensive old workings covering about 1km x 1km. These include at least 200 shafts, many greater than 30m deep as well as at least 30 adits. Many of the adits appear to be in good condition. Some open/collapsed stopes are also visible. By modelling the topography, old shafts and adits it is estimated that previous mining extended to a maximum depth of 100m below surface.
A visit by a USGS geologist in 1974 (Shawe, 1984) provides some brief descriptions and indicates that some very high-grade tungsten mineralisation was being mined at the time. It is difficult to estimate average mined grade for Khao Soon. However, based upon the extent of previous mining and estimated concentrate production, then average grades of 2-4% WO3 are not unreasonable. Shawe 1984, states:
“only the highest grade ore was being mined, both in the principal mine and in numerous small squatter’s mines, and a large amount of lower grade material has been left in the ground”.
Modern exploration at Khao Soon was initiated by Thai Goldfields (TGF) from 2006-2014. Much of this work was led by Australian geologists. TGF conducted surveying of old workings, extensive soil and rock-chip sampling and mapping across much of the project area. This work identified numerous areas with significant tungsten enrichment in soils which in many cases is supported by rock chip sampling and prospective geology. The presence of old workings is also relatively common.
TGF also conducted shallow air core drilling (64 vertical holes for 1540m) at two selected targets. This work identified relatively large areas of near surface, generally low-grade tungsten mineralisation developed in a thick laterite profile. Better WO3 intersections from Target 2 included: 12m @ 0.21% WO3 from 9m, 15m @ 0.15% WO3 from 15m, 11m @ 0.32% WO3 from 9m and 12m @ 0.15% WO3 from 12m.
Locally tungsten mineralisation extended into bedrock beneath the laterite. However, most holes stopped very soon after bedrock was intersected.
Geology and Mineralisation.
The Khao Soon project occurs within the Central Belt of the South East Asian Tin – Tungsten Belt. The Central Belt is responsible for significant historical tin and tungsten production tungsten.
The project area is dominated by a sedimentary sequence consisting primarily of a siltstone with minor sandstone and calcareous inter-beds of the Silurian-Carboniferous aged Tanaosi Group. The large Triassic-Jurassic aged Khao Luang granite batholith intrudes the sedimentary sequences immediately north and west of Khao Soon.
Primary mineralisation in the old mine is hosted within brecciated-fractured silicified sediments. Tungsten occurs as ferberite (FeWO3), an iron rich end member of the wolframite group. Ferberite commonly forms the matrix of the mineralised breccia in association with un-mineralised clasts of silicified metasediment. The breccia appears to be hydrothermal in nature and forms a series of semi-continuous/interconnected pipes, pods, lodes and fracture fill zones. Pyrite occurs in association with the mineralisation and can be locally abundant (Shawe, 1984).
The old Khao Soon Mine workings are scattered over an area about 1km long and 1km wide. Within this area there are three main areas of old workings. The Western Zone, the Central or Main Zone and the Eastern Zone. There are also many other zones of mineralisation associated with old workings identified throughout the project area. In western parts of the project area several prospects returned significant antimony values in rock chip samples with or without associated tungsten.
It is interpreted that the tungsten mineralisation at Khao Soon is related to (sourced from) a younger non-outcropping granite. Regional magnetic data suggests the granite occurs beneath much of the Khao Soon project area and intrudes the sediments and the Khao Luang batholith. The exact depth to the top of the granite is unknown but could be in the order of 1km. Importantly, tungsten mineralisation may occur all the way from the sub-surface granite to the surface. Other styles of mineralisation may also be present with increasing depth.
The Khao Soon project also exhibits areas of extensively developed regolith hosted tungsten mineralisation, including, tungsten in thick lateritic profiles commencing at or very near surface and tungsten in weathered breccia up-dip of fresh mineralisation. The highly anomalous WO3 values in lateritic regolith or weathered breccia at surface are likely vectors to underlying hard rock WO3 mineralisation.
Pan Asia Metals’ work
Pan Asia commenced exploration at the project in late 2014 and has conducted additional confirmatory and extensional soil and rock chip sampling, mapping programs, Induced Polarisation geophysics and reconnaissance diamond drilling at several targets. The combined results of the exploration work indicate the potential for the Khao Soon to be a globally significant tungsten district.
Results achieved include:
- Numerous WO3 in soil anomalies > 0.1% over 4km long 20-150m wide;
- Numerous elevated to high grade WO3 values in rock sampling at many prospects;
- Soils and rock chips indicate prospective strike length totaling about 10km;
- Tungsten in soil anomalies supported by rock chips and breccia occurrences;
- Reconnaissance drilling has identified mineralisation in many holes extending from surface anomalies; and
- IP geophysics has identified several deep targets that require drilling.
Pan Asia has completed a total of 1912m in 22 holes of diamond drilling at the Than Pho Ridge, Than Pho West, Rabbit and Last Hill prospects. The drilling has been highly successful in discovering near surface intersections containing good tungsten grades over considerable widths.
Some of the better results include:
- KSDD001 – 51.5m @ 0.50% WO3 from 0m, incl. 12.8m @ 1.07% WO3 from 14.8m;
- KSDD003 – 24.3m @ 0.24% WO3 from 25.1m;
- KSDD004 – 41.0m @ 0.26% WO3 from 6.8m;
- KSDD006 – 27.6m @ 0.15% WO3 from 14.4m;
- KSDD012 – 11.6m @ 0.18% WO3 from 6.0m;
- KSDD013 – 8.0m @ 0.19% WO3 from 0m;
- KSDD016 – 7.6m @ 0.30% WO3 from 0m;
- KSDD021 – 14.55m @ 0.47% WO3 from 0m, incl. 7.3m @ 0.62% WO3 from 0m; and
- KSDD022 – 32.2m @ 0.31% WO3 from 0m, incl. 7.5m @ 0.56% WO3 from 17.8m.
The drilling results, supported by surface sampling and mapping, have provided Pan Asia the required information to estimate an Exploration Target in accordance with the JORC Code 2012. The Exploration Target covers four key prospects.
The tonnage and grade potential of the Exploration Target is in the range of:
15 to 29 Million tonnes @ 0.2% to 0.4% WO3