The area of the Mt. Ogden porphyry molybdenum prospect is underlain by units of the Upper Paleozoic Stikine Assemblage. In the immediate area of the prospect, the stratigraphy is intruded by a small stock of quartz diorite (and/or quartz monzonite) of the Late Cretaceous Windy Table Complex. A granite and alkali feldspar granite batholith of the Paleocene-Eocene Sloko-Hyder Plutonic Suite is in contact about 2 kilometres to the east.
The principal country rock is a Permo-Triassic sequence of high rank metamorphics which include Permian limestones, dolomitic limestones with chert, and fine-grained hornfelsed clastic sediments and intercalated volcanics which are largely altered to greenstone and phyllite.
In the mineralized area there are only two basic varieties of high rank metamorphics: a fine-grained, dull green, diopside-epidote-garnet skarn hosting disseminated pyrite, pyrrhotite, magnetite or traces of sphalerite, and a white calc-silicate rock containing calcite, dolomite, and wollastonite or tremolite. These rocks are described as exceedingly hard and are descriptively called tactites. They strike northwest and dip steeply to the northeast.
There are reported to be two Cretaceous intrusive types. One is a series of thin, widely-spaced, light coloured dikes. The mineralized intrusive stock is a light coloured, fine-grained alaskite with quartz and feldspar phenocrysts. The alaskite stock is about 1500 metres wide and 1600 metres long.
Molybdenite occurs in several modes within the alaskite. It occurs as coarse platy crystals in widely spaced sub-horizontal veins; in networks of thin veinlets with light coloured alteration envelopes; along fractures; as rosettes of coarse or medium grains associated with vuggy quartz and as fine interstitial grains. Some of the sub-horizontal veins host accumulations of molybdenite up to 10 centimetres in thickness and are traceable for 30 metres across an exposure. Most of the molybdenum mineralization is confined to the alaskite with only minor mineralization in dykes and fractures within the overlying tactites.
Alteration associated with the molybdenum-bearing veins, in selvages from 2 to 10 centimetres in width, is mainly quartz- sericite, accompanied by fluorite, chloritized biotite, minor pyrite, and occasional sphalerite.
As exposed in an adit, the fracture density varies, with an average of four per metre. Near vertical fractures, generally less than 1 centimetre in width, are the most frequent. A prominent flat- lying joint system, at 2 metre intervals, carries higher grade molybdenite mineralization. Quartz is the main fracture filling with associated chlorite, fluorite, rhodocrosite, and minor scheelite.
Sampling a set of mineralized sub-horizontal fractures in Zone Z averaged 0.24 per cent molybdenite within 3 metre chip samples from approximate 300 metre intervals. Also, drilling in 1979 within Zones M and N returned averages of 0.31 per cent and 0.32 per cent molybdenite, respectively (Nevin, 1979).
Reserves are 217,704,000 tonnes grading 0.3 per cent MoS2; conversion to Mo using the factor 1.6681 (Mining Review - May/June 1981). Both tin and tungsten was not reported present in any significant amounts. Likewise, gold, silver, uranium, lead, and zinc showed no significant values.
Locally, a fine-grained, green, diopside-epidote-garnet skarn developed with wallrocks adjacent to the porphyry stock contains disseminated pyrite, chalcoyrite, magnetite, and sphalerite with silver values. These stratiform gossans in certain metasedimentary units contain mainly pyrite and/or pyrrhotite with irregular clots of dark sphalerite. Also, minor molybdenite, scheelite, and pyrite are found in quartz veinlets that crosscut skarn and hornfels.
Work History
Molybdenite was first reported in the area by a Geological Survey of Canada field party under the leadership of Dr. J.G. Souther in the period 1958-60. The Nan claims were staked for Richard White in 1961 and soon optioned to Totem Minerals Ltd. Geologists K. Valentine and R. Macrae reported work on the claim for Totem in 1961. Work consisted of prospecting and sampling, including sampling from glacial moraines in the vicinity. Molybdenite in coarse quartz veins with rare disseminations in a felsite host was reported. In 1967, Mount Ogden Mines skidded a small drill up the glacier to a drill site north of Mount Ogden (Assessment Report 9085). It is reported that only 12 or 15 metres of sparse and uneconomic mineralization was intersected. It was further reported that Mount Ogden Mines completed an airborne EM survey but was of little value in terms of exploration. In 1976, Iskut Silver Mines Ltd. held the ground but allowed the claims to lapse in early 1977. Frank Onucki staked the property later that same year. Nevin Sadlier-Brown Goodbrand Ltd. examined the Moly-Taku claims on behalf of Marge Enterprises Ltd. in 1977. The claims were subsequently optioned to Omni Resources Inc. after preliminary mapping and sampling in 1978. Ninety-six bedrock samples were taken by Nevin Sadlier-Brown Goodbrand Ltd. for Omni at that time. In 1978, Bema Industries sampled and proved the existence of a large, low grade area of molybdenite mineralization. In 1979, Omni Resources Inc carried out a program of drifting and diamond drilling on the N and Z zones. One hundred and fifty-nine metres of drifting and 589 metres of underground drilling failed to substantiate earlier indications of a sizeable orebody. A small high-grade vein, the Serious vein, was found and an estimate of 27,213 tonnes of 1.85 per cent MoS2 was made (Assessment Report 9085). This resource estimate was calculated prior to the implementation of National Instrument 43-101 and is not compliant with those standards. Underground work has not substantiated the surface sampling, however, only a very small portion of the favourable ground has been tested. A 380-metre drill hole on the Z zone failed to intersect economic grade molybdenite mineralization.
Exploration focus prior to 1980 was on zones DD, G, L, M, N, O, P, Q and Z. A new molybdenite-bearing zone, the Y zone, was found late in the 1979 season about 750 metres south of the area that had been previously been examined in detail (Assessment Report 9085). A drill was moved to a site on a ridge above the showing and two holes were drilled.
Doublestar Resources Ltd. acquired an interest in the property in 1998.
Refer to the Moly Taku Y zone (MINFILE 104K 047) for further geological details.
