Mount Pleasant Mine

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Mine TypeUnderground
  • Tungsten
  • Molybdenum
  • Zinc
  • Tin
  • Indium
  • Bismuth
Mining Method
  • Open stoping
Mine Life... Lock


Adex Mining Inc. 100 % Direct

Deposit type

  • Porphyry


There are three main mineralized zones at Mount Pleasant, namely: the Fire Tower Zone, Saddle Zone and North Zone, from south to north. At depth, the Fire Tower and North Zones have been subdivided as shown in a schematic longitudinal section (Figure 15).

The Fire Tower Zone and North Zone deposits are located approximately 1.0 km apart and are mostly less than 400 m vertically from surface. The Fire Tower Zone contains predominantly large (low grade) tungsten-molybdenum deposits and was previously mined underground for tungsten. Some small indium-bearing tin-base metal zones are also present. The North Zone contains the most important indium-bearing, tin-base metal "resources" outlined to date along with some poorly defined low-grade tungsten-molybdenum bodies (ADEX 1995). The Saddle Zone, located approximately halfway between the Fire Tower Zone and the North Zone, contains tin and some base metals and newly discovered tungsten-molybdenum mineralization.

North Zone
The tin and porphyry tungsten-molybdenum deposits of the North Zone represent two different periods of mineralization even though they overlap spatially. Indium-bearing tin-base metal zones in the North Zone appear to be principally associated with sphalerite and are more concentrated in the Deep Tin zone (Figure 16). The principal metallic minerals in these deposits are cassiterite, arsenopyrite, lollingite, sphalerite and chalcopyrite with lesser amounts of stannite, pyrite, marcasite, galena, wolframite, molybdenite, tennantite, chalcocite, bornite, native bismuth, bismuthinite and wittichenite.

Saddle Zone
Tin-base metal mineralization was discovered in the Saddle Zone during a 1988 surface drilling program that was initiated by Lac Minerals because tin mineralization was encountered underground, during development work between the Fire Tower Zone and the North Zone (Sinclair 1994). A 40-metre section in hole LNZ-15, within Granite IIA, graded 0.33% Sn. Subsequently, NovaGold Resources intersected a 16-metre section, also within granite, of 1.31% Sn in drillhole NMR-89-1; this hole also intersected W-Mo-Bi mineralization within quartz-feldspar porphyry adjacent to this granite (Sinclair, 2011). Holes drilled during the 2011 campaign show that tin mineralization has greater extent than previously known (Figure 19) and that tungsten-molybdenum mineralization is also present.

Fire Tower Zone
The Fire Tower Zone is a tungsten-molybdenum deposit that contains three distinct zones: Fire Tower North, Fire Tower West and Fire Tower South. The tungsten-molybdenum deposits in the Fire Tower Zone mainly occur in the lower part of the breccia pipe and the upper part of the underlying fine-grained granite, and to a lesser extent in associated volcanic rocks (Kooiman et al, 2005). These low-grade porphyry-type deposits are characterized by extensive stockworks of mineralized fractures and quartz veinlets. Higher grade zones occurring in areas of intense fracturing measure 200 to 300 m across and as much as 100 m in vertical extent. The high-grade zones are surrounded by lower-grade zones that are characterized by more widely spaced fractures that extend for hundreds of metres into the surrounding rocks.

Mineralization occurs as veinlets and disseminated grains in breccias mainly located within the Mount Pleasant porphyry. The principal "economic-type" minerals are fine grained wolframite and molybdenite, along with minor amounts of native bismuth and bismuthinite.
The gangue minerals consist of cassiterite, arsenopyrite, lollingite, quartz, topaz and fluorite. Multi-stage mineralization is indicated by crosscutting relationships between mineralized fractures and veinlets. Sparse molybdenum-bearing fractures in fine-grained granite appear to represent the final stage of mineralization associated with crystallization of this granite. Finally, the tungsten molybdenum deposits appear to predate crosscutting dykes of unmineralized granite porphyry that truncate mineralized stockwork zones.

Some small indium-bearing tin-base metal zones are also present. The characteristics of the indium-bearing tin-base metal deposits hosted within the Fire Tower Zone have been best described by Kooiman et al. (2005). These deposits occur as irregular veins and mineralized breccias that are irregularly distributed throughout the Fire Tower Zone and are associated with altered and mineralized granite porphyry dykes. Throughout the Fire Tower Zone, the tin-base metal deposits either crosscut or truncate tungsten-molybdenum stockworks. In general, veins range from 1 to cm in width and up to several metres in strike length. In places, larger veins up to 10 m in width and 100 m long can occur. Veins pinch and swell along strike and contain abundant chlorite and fluorite and disseminated massive sulphides.

Mineralized breccias are irregular bodies and occur as small vertical circular pipes up to 10 m wide and 100 m in vertical extent. These breccias can contain fine-grained sulphides and cassiterite as well as chlorite and fluorite.

The indium-bearing tin-base metal veins and breccias contain the principal oxide minerals cassiterite and wolframite. Sulphide mineralization consists mainly of sphalerite, chalcopyrite, galena and arsenopyrite and minor amounts of pyrite, lollingite, molybdenite, tennantite, native bismuth and bismuthinite.



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Mine Management

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