The Monte Cristo (L.802) occurrence is located at an elevation of approximately 1230 metres on the western side of Monte Cristo Mountain and north of the community of Rossland.
Regionally, the area is underlain by Lower Jurassic Elise Formation (Rossland Group) siltstone, argillite and hornfelsed siltstone, which is intruded by quartz monzonite of the Early Jurassic Rossland Plutonic Suite. The grey to black siltstone and argillite grades into hornfels and forms distinct layers within the volcanic breccias, and several horizons grade laterally into sandstone and breccia. Small Early Jurassic ammonites are reported to occur in the siltstone on Ivanhoe Ridge. The Rossland Group rocks are crosscut by north trending lamprophyre and diorite dikes hosting disseminated pyrite.
The Monte Cristo veins are part of the ‘North belt’ zone of discontinuous veins in the Rossland mining camp. On a regional scale, the veins appear continuous but in detail they are lenticular and offset by north-trending faults. The veins strike east-west and dip between 70 to 75 degrees north. Refer to the Le Roi (MINFILE 082FSW093) deposit for a summary of the Rossland mining camp.
The vein is hosted by the Early Jurassic Rossland monzonite, a biotite-hornblende-augite monzonite stock that is medium-grained, grey to green and hosts magnetite; apatite and some sphene chlorite, epidote, pyrite, and pyrrhotite. The stock intrudes siltstone, argillite, hornfels and volcanic conglomerate of the Lower Jurassic Elise Formation (Rossland Group). Lamprophyre dikes and swarms of diorite dikes crosscut the monzonite and host disseminated pyrite.
Mineralization in the vein consists of massive banded pyrrhotite with chalcopyrite and pyrite. Pyrite occurs as crystals in the pyrrhotite and as disseminations in the hostrock. The pyrrhotite is auriferous and contains nickel with a trace of cobalt. Cobaltite is also found in the ore.
Tunnel No. 1 was driven at elevation 1230 metres along the main vein, which strikes east-west and dips 75 degrees north with an average width of 0.76 metre. The sulphide shoot occurs along a major fault and is cut off by a crosscutting sericitic diorite dike.
Tunnel No. 2, at elevation 1194 metres, was driven west along a vein that dips 70 degrees north. This tunnel connects with Tunnel No. 1, and a 25-centimetre streak of arsenopyrite was noted in the raise with the pyrrhotite. The shallow underground workings are developed within the northern contact zone of the Rossland monzonite.
In 1915, an ore sample from the Tunnel No. 2 vein assayed 27.08 grams per tonne gold, whereas a sample of the pyrrhotite gave 0.13 per cent nickel oxide and trace cobalt (Geological Survey of Canada Memoir 77, page 109 and 75).
In 1986, a 1 square-metre panel sample (83124C) assayed 1.3 grams per tonne gold, whereas a 0.75 metre chip sample (83125C) yielded 1.7 grams per tonne gold (Assessment Report 15432).
The area has been explored since the late 1800s, with the Crown-granted mineral claims being staked in the early 1890s. Development work around this time comprised at least two tunnels or adits, a shaft and numerous pits or trenches.
In 1979, Cominco Ltd. completed a program of rock and soil sampling on the area. During 1982 through 1986, Gallant Gold Mines Ltd. completed programs of rock and silt sampling, geological mapping, ground geophysical surveys and seven diamond drill holes, totalling 694.0 metres, on the area as the Georgia property.
