The Nettie M occurrence is located 2.5 kilometres east of Toby Creek in the Golden Mining Division. The occurrence is at 1710 metres elevation above sea level on the north face of Coppercrown Mountain of the Purcell Mountains.
The area is underlain by Proterozoic clastic sedimentary rocks and Cretaceous intrusive rocks. The occurrence is within the Dutch Creek Formation of the Proterozoic Purcell Supergroup. The Purcell Supergroup strata include the Aldridge, Creston, Kitchener, Dutch Creek and Mount Nelson formations (Paper 1990-1).
In the vicinity of the occurrence, rocks of the Kitchener and Dutch Creek formations have been further subdivided and assigned to the Van Creek and Gateway formations (Open File 1990-26).
The Dutch Creek Formation includes green and black laminated argillite, quartzite, siltstone and buff dolomitic siltstone. The Van Creek Formation consists mainly of coarse to medium grained, light grey to dark green quartzite, siltstone and silty argillite and correlates with the strata of the Lower Kitchener Formation.
The Gateway Formation consists of an interbedded sequence of quartzite, green siltstone and buff dolomite that correlates with the lower portion of the Dutch Creek Formation. The contact with the underlying Van Creek Formation is gradational or marked by the basaltic flows of the Nicol Creek Formation.
The sedimentary rocks have undergone regional metamorphism to at least greenschist facies.
On the Nettie M occurrence, the Gateway Formation consists of black siltstone, buff coloured dolomite and minor quartzite. The occurrence consists of a quartz vein that follows a north-trending fracture or fault. The vein has an average width of 30 centimetres but does exceed 1 metre in places. Mineralization consisting of galena with minor chalcocite occurs in white quartz.
The vein has been explored with seven small adits. Past production from the occurrence yielded 261,483 grams of silver, 591 grams of gold, 19,141 kilograms of lead and 3170 kilograms of copper from 61 tonnes mined.