(Volcanogenic Massive Sulphide) Copper Deposit
The Karchiga Cu deposit is located in the Kurchumskiy Raion (district) of East Kazakhstan Oblast (region), 250km southeast of the regional administrative centre of Ust-Kamenogorsk and 120km southeast of the town of Kurchum. Geographical coordinates for the deposit are 85°12.5’E and 48°30’N. The Chinese-Kazakh border is situated 40km to the east and the Irtysh River 50km to the south. The nearest settlement, Altai village, is 8km from the deposit and accommodation is provided in Karoi village, situated approximately 24km from the deposit.
The Karchiga Cu deposit is located within the Vavilon-Karchiga zone of the northwest striking, mid-Palaeozoic, Rudny Altai VMS belt, the host of numerous world-class VMS deposits, including Leninigorsk, Zyryanovsk and Maleevsky. The Rudny Altai VMS terrane is ranked in the top four VMS belts of the world.
The deposit was rediscovered in 1913 and further explored in 1936. It was then actively explored in 1941–1942, when the first resource estimate was completed. In the 1950s it was extensively explored by Soviet expeditions. The Soviet era exploration included:
- Diamond drilling of 104 holes totalling 18,463.5m;
- 33 surface trenches totalling 1,970m; and
- A 40m deep exploration shaft and limited underground development including a small drift less than 20m horizontally from the base of the shaft.
The work culminated in 1956 with the submission of a report to the USSR State Reserves Committee with an estimate of C1+C2 ‘reserves’ totalling 6.3Mt at a grade of 2.77% Cu and 0.8g/t Au. This estimate of ‘reserves’ and metal content was approved by protocol No. 1639, dated 14 February 1957, by the USSR State Reserves Committee, totalling 5.11Mt in the B (376kt), C1 (3.646Mt) and C2 (1.09Mt) categories at a grade of 2.77%Cu, 0.79g/t Au and 5.5g/t Ag.
It should be noted that the Soviet era ‘reserve’ estimates were not reported in accordance with the guidelines of either the JORC Code (2004) or National Instrument 43-101 and have not been validated in detail by either Orsu or WAI.
The Karchiga Contract was granted on 16 January 2006 by the Ministry of Energy and Minerals Resources of the Republic of Kazakhstan based on the positive outcome of the Tender Committee hearing. The final registration of the Contract with the State Committee for Subsoil Use was granted on 28 February 2007.
The Contract area has had no previous ownership history and was granted directly by the Ministry of Energy and Minerals Resources of the Republic of Kazakhstan.
Since the granting of the licence in 2007 Orsu has completed 13,827m of HQ Diamond Drilling, 83.15km of DP-IP geophysical surveys, in excess of 1,000m of surface channel sampling and collected and assayed 3,600 soil geochemical samples.
The Karchiga deposit is hosted by a conformable series of amphibolite units with the dominant mineralogy comprising gruneritic amphibole, feldspar and quartz (Herrington and Stanley, 2008) and ranging in thickness from 50 to 100m; these alternate, with what have been identified as biotite gneisses (also referred to as quartz-mica schists) within a northwest-striking sequence, that dip northeast at 30-60°. Both units demonstrate a strong schistosity that is generally layer parallel, though the biotite gneiss is highly refolded locally. The amphibolite schists are less deformed and the schistosity remains sub-parallel whilst being more resistant than the biotite gneiss and therefore forming a series of prominent dark layered amphibolite northwest-striking ridges upon one of which the deposit is situated.
The Karchiga deposit is classified as a metamorphosed Volcanogenic Massive Sulphide (VMS) deposit with Copper as the primary economic element of interest. VMS deposits are also known as volcanic-hosted, volcanic-associated, and volcano-sedimentary-hosted massive sulphide deposits. They typically occur as lenses of polymetallic massive sulphide that form at or near the seafloor in submarine volcanic environments. They form from metal-enriched fluids associated with seafloor hydrothermal convection. Their immediate host rocks can be either volcanic or sedimentary. VMS deposits globally are major sources of Zn, Cu, Pb, Ag and Au, with significant amounts of Co, Sn, Se, Mn, Cd, In, Bi, Te, Ga and Ge and, in some cases, As, Sb and Hg.
VMS deposits form through the focused discharge of hot, metal-rich hydrothermal fluids and therefore are classified under the general heading of "exhalative" deposits.