At the Monte Carlo showing, disseminations and veinlets of pyrite, chalcopyrite and magnetite occur in partly albitized porphyritic microdiorite. The intrusive rocks are part of the Sugarloaf unit of the Late Triassic-Early Jurassic Iron Mask batholith.

By 1904, three groups of claims were located in the area of which the Monte Carlo formed part. The first development work reported on the Monte Carlo was in 1905. G.J. Rogers, of Knutsford, owned the Monte Carlo claim in 1913. A shaft was sunk to a depth of 18.2 metres. In 1929, The Consolidated Mining and Smelting Company of Canada, Limited completed 27.4 metres of drifting in an adit. The shaft is about 55 metres southeast of the adit. In the same year, three diamond-drill holes totalling 243.8 metres were drilled between the shaft and adit but mineralization was not intersected due to crossfaulting. In 1952, four diamond-drill holes were drilled in the vicinity of the Monte Carlo claim by Berens River Mines Limited. At least two of the holes were drilled midway between the Wheal Tamar (092INE013) and Monte Carlo adits. None of the holes intersected significant mineralization. In 1967, Cominco Ltd., as part of a larger program on the Ajax East or Wheal Tamar deposit, drilled one hole (No. 52) on the Monte Carlo claim and intersected low grade copper mineralization in altered porphyritic Sugarloaf unit microdiorite at 5.7 to 23.7, 35.0 to 49.9, 71.0 to 89.0, and 115.2 to 124.3 metres. The hole was drilled to 154.5 metres depth in a northeasterly direction and ended in picrite basalt. In 1967, drilling was reported on the Wheal Tamar and Monte Carlo showings. In 1980, Cominco Ltd. completed seventy-four percussion-drill holes on their Ajax property of which eight holes were drilled on the Monte Carlo claim. All eight holes intersected varying amounts of copper mineralization.