The Maggie porphyry copper-molybdenum deposit is associated with a Tertiary biotite quartz monzonite porphyry stock (Maggie stock) that intrudes weakly metamorphosed sedimentary and volcanic rocks of the Carboniferous-Jurassic Cache Creek Complex. Economic mineralization is largely confined to the stock but also extends into Cache Creek rocks.
The Maggie stock is approximately 1500 metres long and 425 metres wide, but does not outcrop. While much of the stock is homogeneous, a fine grained quartz diorite border phase is recognized along its margins. The stock is covered by 45 to 120 metres of till and alluvium and is cut by a number of premineral latite porphyry dikes. At some distance from the stock, several light coloured porphyritic dikes and small intrusions varying in composition from quartz latite to diorite, intrude the Cache Creek rocks.
Cache Creek strata exposed along the walls of the Bonaparte River valley strike mainly northwest and less commonly northeast, and dip both east and west at moderate to steep angles. Near the Maggie deposit, drill core indicates Cache Creek rocks dip at moderate angles. An anticlinal structure in the Bonaparte Valley is suspected, with the Maggie stock lying to the west of the anticlinal axial plane. The Maggie stock and several dikes trend northwest. Shear zones and a number of small ultramafic bodies trend northeast and dip steeply southeast or northwest. Some ultramafic bodies trend northwest and dip southwest.
The Cache Creek Complex comprises interbedded chert and argillite, limestone and intermediate to mafic volcanic rocks which are intruded by a number of small serpentinized ultramafic bodies. These sill-like intrusions are cut by the Maggie stock or occur as large inclusions within it. The ultramafic rocks within the deposit are weakly mineralized with chalcopyrite and commonly contain fine grains of pentlandite.
Tertiary Kamloops Group basaltic to andesitic flows and breccia crop out east of the deposit where they are in fault contact with the Cache Creek strata. Diamond drilling indicates the Tertiary rocks are downfaulted a couple of hundred of metres with respect to Cache Creek rocks.
The Maggie deposit comprises low grade chalcopyrite-molybdenite mineralization in an elongate zone trending 323 degrees and dipping steeply toward the southwest. The long dimension is 1280 metres and its maximum width is 365 metres. The deposit contains two deeply rooted core zones with relatively high-grade mineralization which are surrounded by areas of shallower, lower grade mineralization. The principal host of the mineralization is the biotite quartz monzonite porphyry stock (Maggie stock). To a lesser extent, economic minerals occur in related intrusions, dikes, Cache Creek rocks and ultramafic bodies adjacent to the stock. Inclusions of older rocks and dikes cutting the stock are also mineralized.
Ore minerals comprise generally fine-grained chalcopyrite and molybdenite. These minerals occur in three principal associations: (1) fine disseminations in quartz veins; (2) fine disseminations throughout the hostrock; and (3) fine veinlets within or bordering quartz or, less commonly, calcite veins. The first two associations are approximately equally common while the third is less common and typically occurs near the edges of the deposit.
Rare bornite is reported only in the central part of the deposit. Tennantite was also reported in drill core as 2-4 millimetre wide veinlets and is concentrated at the periphery of the deposit.
Both copper and molybdenum grades decrease outward from two higher grade central areas. Similarly, the vertical distribution of these minerals is related to the two central cores. Within the core regions, mineralization persists to depth whereas in adjacent zones mineralization is relatively shallow.
Pyrite is the most common sulphide associated with the deposit and varies in content from 1 to 3 per cent in the central part of the deposit to over 10 per cent in a well-developed peripheral halo. In the central zone, pyrite is disseminated throughout the hostrock and, to a lesser extent, occurs in veins. On the margins of the deposit, however, pyrite in veinlets is as prominent as it is disseminated. The pyrite halo contains 1 to 14 per cent pyrite over widths of 450 to 750 metres east and west of the deposit and extends even greater distances north and south of it.
Quartz veining is prominent throughout and commonly constitutes 5 to 20 per cent of the rock. Calcite veining is less common and is generally restricted to the margins of the deposit.
The Maggie stock and bordering Cache Creek rocks have been pervasively modified by hydrothermal alteration. Overlapping potassic/phyllic alteration assemblages are associated with the two northwest trending core zones in the deposit. Within these zones plagioclase is almost completely altered to sericite, potassium feldspar and kaolinite; potassium feldspar is partly altered to biotite, sericite and secondary potassium feldspar; and biotite is altered to secondary biotite, sericite and rutile-leucoxene aggregates. The best grade mineralization is found within these core zones.
Outward from the core zones, alteration zones are complex and do not fall into simple annular patterns. Various overlapping phyllic, argillic and potassic alteration assemblages are present and associated chalcopyrite-molybdenite mineralization is relatively low grade. Argillic alteration is well developed in a northwest trending area between the two core zones. In this area, plagioclase is almost completely altered to kaolinite, sericite-illite and minor potassium feldspar. Primary potassium feldspar is virtually unaltered and biotite is altered to secondary biotite and sericite.
Strong phyllic (sericitic) alteration is associated with the western border phase of the Maggie stock. Plagioclase and biotite are completely altered to sericite and potassium feldspar is absent or present in minor amounts. Strong quartz-pyrite veining and very sparse chalcopyrite-molybdenite mineralization, mainly in quartz veins, are present.
Outward from the stock, bordering Cache Creek rocks and small felsic intrusions have sustained variable degrees of alteration. Drill core indicates strong alteration occurred laterally a distance of about 90 metres beyond the stock, then decreased gradually to almost nothing about 600 metres from the stock. Bordering the stock, argillites have been converted to rocks composed essentially of interlayered biotite and quartz; cherts to quartz-sericite aggregates; volcanic rocks are variably replaced by biotite, chlorite, epidote, sericite, quartz, calcite and other minerals; and small felsic intrusions have been affected by quartz-sericite-biotite alteration. In the outer part of the contact zone, the predominant alteration minerals are chlorite, epidote and calcite.
Surrounding the Maggie deposit are extensive gossans which have developed from the oxidation of the pyritic halo. Weathering has leached most of the sulphides from the gossan zones to a depth of approximately two metres.
In 1970, drilling outlined a deposit containing indicated reserves of 181,440,000 tonnes grading 0.28 per cent copper and 0.029 per cent molybdenum (Canadian Institute of Mining and Metallurgy Special Volume 15 (1976), page 329).
The Maggie claim is reported to have been staked in the 1890s by a Mr. Hocking. In about 1896, the B.C. Development Company, Limited acquired the Avoca, Avon, Amazon, Ankobra, Atrato, Atarboo, Arkansas, Axim, Alabama Fr., Athabaska Fr., Assiniboine Fr. and Amoor Fr. claims (Lots 410-421) covering a large conspicuous gossan zone. The relationship of this claim group to the Maggie claim is not clear. Apparently the Maggie claim was located on showings associated with a shear zone adjacent to the gossan zone. The Avoca, etc. claims were Crown granted to the company in 1898. Considerable exploration and development work was done on the Maggie property prior to 1905. A shaft was sunk about 81 metres and approximately 305 metres of drifts and crosscuts were driven on three levels; the upper (No. 1) level was driven at road level and connected to the shaft by a short crosscut. About 457 metres southwest of the shaft workings, two crosscuts were driven to prospect a zone of crossfracturing. In 1907, the Maggie claim was owned by Messrs. Hocking, Smith and Bryson. Work during the year, by Messrs. Rombauer and Adams, who held the property under bond, included stoping over a length of 21 metres and a height of 9 metres on No. 2 level, and rehabilitation work on No. 3 level. In 1907, 41 tonnes of sorted ore was shipped from the property. No further activity was reported until 1915 when W.J. Milne & associates of Vancouver, bonded the property. Work was begun by the Golden Gate Mining Company, Limited but little was accomplished other than pumping out the workings. The property was idle again until 1929 when J.C. Hocking, son of the original owner, and J.B. Bromley reported some assessment work. They also held a lease on three of the Crown-granted claims. The old workings were dewatered in 1930 but nothing further was done.
In about 1952, Kennco Explorations Limited is reported to have put down three drillholes on the property. In 1963-64, Frobex Limited held, jointly with Tache Lake Mines Limited and Metal Mines Limited, two Crown grant leases and fifty-four claims. A small amount of drilling during this period is reported to have cut low values over considerable widths. In 1968, Bethlehem Copper Corporation acquired the property (Eiggam Group) comprising Mineral Lease 33R (Lots 410-421) and 10 recorded Beth claims; the M claims were subsequently staked for a total of 68 claims.
In 1968, percussion drilling totalled 227 metres in five holes. Work in 1969 included geological mapping and 453 metres of diamond drilling in one hole. Drilling in 1970 on the valley floor, to the east of the gossan zone, intersected a mineralized zone. To the end of 1971 drilling totalled fifty-seven percussion holes (5163 metres) and thirty-two diamond-drill holes (12,939 metres). In 1972, a further 825 metres of diamond drilling in two holes was done to test the southeast extension of the mineralized zone. Topographic mapping was carried out in 1973 and 1974. Work in 1975 included 610 metres of diamond drilling in two holes. Additional work in 1977-78 included an induced polarization survey over 1.2 kilometres and 53 metres of drilling in an attempt to deepen a previous hole.
