Lupin is located on the shores of Contwoyto Lake at lat. 65° 48’N, Long. 111° 15’W and lies about 80 kilometres south of the Arctic Circle. Since start up in 1982 the mine has produced over 2.15 million ounces of gold from 6.66 million tonnes of ore grading 10.63 gm/tonne. Total remaining reserves at 1993 year end were 5.1 million tonnes at a grade of 9.11 gm/tonne (1.65 million ounces). This is sufficient for 7 – 8 years at the present annual production rate of about 200,000 ounces. The Centre and West Zones of the deposit are open to depth.

Controls of Gold and Sulfide Distribution at Lupin NWT

Different processes have been suggested for the formation of the Lupin deposit including synsedimentary deposition of gold and sulfides, epithermal emplacement of gold, metasomatic emplacement of gold and sulfides, redistribution of gold and sulfides during metamorphism and combinations of the above. There is no unequivocal argument in the literature for any of the possibilities noted, although different authors have their own biases. The geological staff at Lupin deals with the deposit on a daily basis over long periods of time and

Excluding economic factors, the physio-chemical parameters of ore deposits such as permeability and mineralogy constrain the application of ISM techniques to those ores that can be readily accessed by a suitable lixiviant and dissolved. The released metals must then be transported to the surface in solution. Most mineral deposits are geologically complex and evaluating their in situ mining potential in a quantitative or even a semi-quantitative fashion is a formidable task. It is important, however, to characterize the geology of a deposit as completely as possible because such information (particularly the microscopic characteristics) is vital to the successful engineering of an ISM operation.

Geocharacterization of the deposit should be carried out at all scales. Large scale studies such as the collection of major fracture and fault densities and orientations are used to evaluate the hydrologic properties of the deposit. Fluid infiltration and migration through fracture networks in crystalline rock can be modeled using these data (Neuman, 1986). The distribution of host-rock lithologies and ore bodies should be mapped in detail in order to evaluate ore reserves and to select proper well placement, and depth of injection. Small scale studies describe the

Stratigraphy

The stratigraphic sequence in the Carlin Trend Geological area is Lower Paleozoic marine sediments and Late Tertiary tuffaceous sediments. The Lower Paleozoic sediments consist of the Siluro-Devonian Roberts Mountains Formation, the Devonian Popovich Formation and the locally named Rodeo Creek Formation. The Rodeo Creek Formation had previously been described in the mine area as the Ordovician-Silurian Vinini Formation, which had been thrust over the Popovich Formation along the Roberts Mountains Thrust. This is now thought to be erroneous due to the lack of structural evidence for thrusting, the gradational nature of the contact between the Popovich Formation and Rodeo Creek Formation and the presence of Mid to Upper Devonian age radiolaria and conodonts in rocks above the Popovich Formation.

The Lower Paleozoic units are a transgressive sequence of carbonate shelf, slope, and basin facies that have gradational contacts. The Roberts Mountains Formation consists of carbonaceous calcareous siltstones to fine grained sandstones. It is only found in the subsurface at depths of 1,400′ to 1,500′ in the extreme northern part of the mine area. The Popovich Formation can best be described as a sequence of dirty, limestone. It occurs at

Worldwide, diatomites occur within Tertiary to Recent lacustrine and marine sediment facies (see Table 1). Geologically, the oldest marine and lacustrine diatoms predate the effusive blooms of the post Oligocene depositional period, and are respectively found within Cretaceous and late Eocene sediments. In the U.S., marine species are found in rocks as old as the California’s Cretaceous Moreno Shales. The oldest non-marine diatoms observed in the U.S. are found as a well developed assemblage within late Eocene sediments of Wyoming.

Deposits of diatomite reflect stability of environmental and depositional conditions as well as optimum preservation environment. While depositional rates vary, typical varve thicknesses suggest yearly accumulations of no more than several millimeters of compacted sediment. Strata of significant thickness and high purity, therefore, indicate prolonged environmental conditions that favored high diatom productivity and that were free of continuous and significant elastic contribution or chemical precipitation. Geological preservation of the soft sediments requires protection from erosion, such as by overlying volcanics, and it also demands that they are not subjected to geological conditions which promote dissolution or diagenetic alteration to chert, porcelanite or quartz such as deep burial, exposure to high