Summary:
The Property contains a tungsten skarn deposit; skarns are contact metasomatic deposits, exploited for tungsten, with accessory molybdenum, copper, tin and zinc.
The tungsten mineralisation of the Sangdong deposit is contained in several tabular, beddingconformable skarns in the Myobong Shale; these skarns have been interpreted as comprising carbonate-bearing horizons that were altered and mineralised by fluids ascending from the underlying Sangdong Granite.
From uppermost to lowermost, these horizons are termed the Hangingwall, Main, and Footwall horizons. Calc-silicate layers from 0.50 – 1.0m in thickness have developed on the upper and lower contacts of the Main and Footwall horizons.
The Hangingwall horizon is located near the upper contact of the Myobong shale and varies in thickness from approximately 5.0 to 30.0m because of the irregular boundary of the shale with the overlying Pungchon Limestone. This zone has a strike length of about 600m and a down-dip extent of about 800m. Above the most highly-altered portion of the Main horizon, the Hangingwall horizon is not tabular, but extends steeply and irregularly into the overlying limestone. The Hangingwall horizon contains diopside, garnet, fluorite, zoisite, quartz, hornblende, wollastonite and up to 50% calcite and although there is some zonal variation in mineral assemblages (diopside-, hornblende- and quartzrich zones) the zonation is not as well- developed as in the underlying Main horizon. The tungsten values show some zonation and decrease in value up-dip. The base of the Hangingwall horizon is approximately 14m above the upper contact of the Main horizon.
The Main horizon strikes about 100° and dips northerly between 15° and 30°. The strike length is in excess of 1,300m and thickness varies from 5.0 – 6.0m. Alteration (skarnification) within the Main horizon forms three concentric, roughly circular zones. A central quartz-rich zone consisting of muscovite, biotite, quartz and minor chlorite is about 350m in diameter and plunges down the Main horizon at N05°W and is coincident with the higher tungsten grade portion of the deposit. The central zone is succeeded outward by a hornblende-rich zone containing diopside, hornblende or tremolite, chlorite, fluorite and calcite. A diopside-rich zone occurs both horizontally beyond and stratigraphically above the hornblende-rich zone and contains garnet, diopside, quartz, fluorite, zoisite and plagioclase. The diopside zone is typically poorly-mineralised. Boundaries between these zones are diffuse and transitional.
The Footwall horizons comprise multiple layers: Footwall Zone 1 (F1) occurs 1m below the Main horizon and is approximately 2m thick; Footwall Zones 2 and 3 (F2, F3) are situated approximately 35.0 to 40.0m below the Main horizon and are less than 1m thick. Further Footwall Zones have been identified beyond F3 and are collectively referred to as F4. Areal dimensions of these horizons and the zonal distribution of calc-silicate minerals in them are similar to those of the Main horizon. F1 has sometimes been mined with extraction of the Main Zone. Some parts of F2 and F3 have been mined in the upper section of the mine.
The Sangdong deposit contains scheelite, minor wolframite, molybdenite, bismuthenite and native bismuth. Molybdenum also occurs in substitution with scheelite and about 30% of the molybdenum produced at Sangdong was scheelite-related. Gold and silver occur in association with bismuthinite and native bismuth and were recovered from the bismuth concentrate. Tellurides, arsenopyrite, pyrite, chalcopyrite and sphalerite also occur.
Mineralisation is largely associated with quartz veins within those horizons, with the exception of the central portion of the Hangingwall horizon. Quartz veins are most abundant within a central, quartzrich portion of the deposit, parallel to and discordant with the calc-silicate layering. Veining ranges from one to ten centimetres in width and is best developed in the lower portions of the mineralised horizons.
The abundance of scheelite within the mined portion of the Main horizon is concentrically zoned, increasing with alteration intensity, depending on temperature. Scheelite abundance in the Hangingwall horizon is more variable and less clearly concentrated in zones.
Molybdenum and bismuth are concentrically zoned in a similar pattern to tungsten in the Main horizon.
The area is cut by steeply north dipping reverse and normal faults which have resulted in offsets of the mineralised horizons by as much as 50-100m.
Sangdong East (“East WO3 Orebody") is located about 1km to the east from the Main deposit. It is essentially an extension of the main mine area, and stratigraphy and lithologies are similar. In contrast, however, the Hangingwall (Upper) horizon, Main horizon, and Footwall (Lower) horizons are thinner, and have a lower frequency of quartz veins. The constituent minerals are pyroxene and garnet with accessory plagioclase, quartz, apatite, hornblende and wollastonite.
In the Sangdong West area (“West WO3 Orebody"), mineralisation and stratigraphy are similar to the main Sangdong Mine, but skarn horizons are thinner, and there is a lower frequency of quartz veining than in the Main horizon. The vein width and grade of tungsten mineralisation do, however, increase northward to the Hwajeolchi area.