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Model Number A-11: Calc-Alkaline Porphyry Copper-Molybdenum-Gold-Tungsten

Concise Description: Fracture-controlled quartz-sulphide veinlets and veins, and sulphide disseminations infractures hosted by, or proximal to, high-level, calc-alkaline, intermediate to felsic, porphyritic intrusions.

Geological Environment

Host Rock Types: Spatial and genetic relationship to high-level (epizonal), calc-alkaline, intermediate to felsicstocks, dykes, sills, and breccia pipes, with porphyritic phases, that are intrusive into volcanic and sedimentaryrocks. These commonly occur as subvolcanic intrusions to volcanic complexes. The porphyritic intrusions and/or thesurrounding country rocks may host the mineralization. Multiple intrusive phases and brecciation are common.

Typical general associations are: quartz monzonite to alkali feldspar granite: Mo-W; granodiorite to quartzmonzonite: Cu-Mo; and diorite-quartz diorite-tonalite: Cu-Au-(Mo).

In Saskatchewan, the Phantom LakeBoot Lake Intrusive Complex near Flin Flon consists of a high-level,multiphase, zoned, granodiorite to granite, porphyritic intrusion. At Amisk Lake, feldspar and quartz porphyritic,dacitic to rhyolitic, multistage dykes occur on Missi Island. Both occur in the Flin Flon Domain.

Rock Textures: Intrusions are medium to coarse-grained phaneritic, with prominent phases that are feldspar, quartz-feldspar, and/or quartz porphyritic, typically with an aplitic groundmass. Various types and styles of intrusive andhydrothermal breccia are very common.

Ages of the Host Rocks and Mineralization: On a world scale they range from Archean to Tertiary. However, mostof the economic deposits are Mesozoic to Tertiary. This is probably related to erosion, in that these deposits aregenerally formed within 5 km of the surface in orogenic belts and the older deposits are more likely to have beenremoved. In Saskatchewan, the known deposits are Paleoproterozoic.

Depositional Environment: High-level (

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very large with dimensions in plan of hundreds to thousands of square metres and a vertical extent of hundreds tothousands of metres.

Alteration: Hydrothermal alteration is extensive, pervasive, and typically zoned, both on a deposit scale and aroundindividual veins and veinlets. Typical alteration assemblages are of four main types: 1) potassic: K-feldspar and/orbiotite +quartz amphibole, anhydrite, magnetite, sericite, and albite; 2) phyllic: quartz, sericite, and pyrite;3) argillic: intermediate assemblagequartz, illite, and pyrite kaolinite, montmorillonite, smectite, and calcite;advanced assemblage kaolinite-dickite, pyrophyllite, alunite, diaspore, and quartz; and 4) propylitic: quartz,chlorite, epidote, and calcite albite and pyrite. Typical zonation consists of an inner potassic zone and an outerpropylitic zone. Phyllic and intermediate argillic alteration are younger and are commonly superimposed betweenthe potassic and propylitic zones, or as irregular to tabular zones superimposed on the older alteration andmineralization. Potassic alteration is typically coincident with the ore zone. In practice the alteration types andpatterns may vary greatly between deposits. Advanced argillic alteration assemblages are often developed in theupper portion of the hydrothermal system and are commonly associated with high-sulphidation epithermalmineralization.

Geological Ore Controls: 1) convergent tectonic settings represented by volcanic island arcs and continental marginarcs; and large-scale continental rifts; 2) associated large-scale, deep-seated, extensional faults; 3) high-level, calc-alkaline, intermediate to felsic, porphyritic intrusions; commonly subvolcanic; 4) formation of extensive andmultiphase fracturing and brecciation; 5) magma-generated hydrothermal fluid transport of metals with deposition,due mainly to a sharp decrease in temperature, in open fractures and breccias; 6) associated extensive, pervasive,and zoned alteration; and 7) ore zones are generally associated with areas of high fracture densities and potassicalteration.

Geochemical Signature: 1) zoned alteration (see Alteration Section above); 2) metal zonation (see MineralogySection above); 3) characterized by a sulphur-rich system; and 4) surficial geochemistry programs for associatedmetals.

Geophysical Signature: 1) airborne and ground magnetic surveys to detect magnetite-rich zones and as an aid tomapping; 2) induced-polarization/resistivity surveys to outline disseminated sulphides; 3) resistivity surveys to helpmap alteration zones; 4) airborne and ground radiometric surveys to help delineate K-rich alteration zones; 5) audio-frequency magnetotelluric surveys to define the limits of the porphyry systems; and 6) short-wave infraredspectroscopy for clay alteration identification in the field.

Examples (with grades and tonnages)

World examples include Butte, Montana; Bingham Canyon, Utah; Highland Valley, B.C.; and Chuquicamata, Chile.

The two recognized examples in Saskatchewan are the: 1) Phantom LakeBoot Lake Intrusive Complex near Flin

Flon with a Au-W-Cu-Mo metal association; and 2) a suite of porphyritic dykes on Missi Island in Amisk Lake thathost a Cu-Mo-Au metal association. Neither has a defined resource.

At the Phantom LakeBoot Lake Complex, pyrite with associated chalcopyrite, and variable molybdenite, scheelite,arsenopyrite, sphalerite, and gold, together with quartz, occur in veins, stockworks, and as sulphide disseminationsin fractures. Alteration is of two types: 1) hematite-quartz-carbonate-epidote (propylitic); and 2) sericite-quartz-carbonate (phyllic). Alteration is pervasive and restricted to the intrusion.

At Amisk Lake, pyrite, chalcopyrite, minor molybdenite, and local sphalerite and pyrrhotite occur within quartz-filled veinlets and as disseminations in fractures within the porphyritic dykes and associated volcanic rocks.Pervasive silicification and sericitization are associated. Propylitic alteration (chlorite, epidote, hematite, carbonate,pyrite) has also been noted.

It has been suggested (Coombe Geoconsultants Ltd., 1991, p47) that some of the gold deposits in the La RongeDomain, particularly in the Waddy Lake area, may have some similarities to the porphyry deposit type.

The 1.76 Ga Nueltin Granite Suite, that contains phases of fluoritic, porphyritic granite and monzogranite, locallyintrudes the Wollaston Domain and the eastern portion of the Mudjatik Domain. These intrusions may have somepotential to contain porphyry Mo-W mineralization. SMDI 0705 is a drill-tested Mo occurrence associated withthese granites in the Mudjatik Domain. Two Mo-U-Th occurrences (SMDI 1135 and 1136) in the Mud Lake areaand two Mo locations (SMDI 1137) at Yurchison Lake in the Wollaston Domain have characteristics of porphyry-style mineralization.

Selected Bibliog raphyCoombe Geoconsultants Ltd. (1991): Base metals in Saskatchewan; Saskatchewan Energy and Mines, Open File

Report 91-1, sections p38-40, 47, 73-74, and 76-78.

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Panteleyev, A. (1995): Porphyry Cu Mo Au, model L04; British Columbia Geological Survey, Mineral DepositProfiles, www.empr.gov.bc.ca/Mining/Geoscience/MineralDepositProfiles.

Pearson, J .G. (1987): Gold mineralization in the Flin FlonAmisk Lake area, Saskatchewan; inGilboy, C.F. andVigrass, L.W. (eds.), Economic Minerals of Saskatchewan, Saskatchewan Geological Society, SpecialPublication No. 8, p37-43.

Rogers, M.C. and Fyon, J.A. (1995): Calc-alkalic porphyry Cu-Mo-(Au-W); inRogers, M.C. Thurston, P.C., Fyon,J.A., Kelly, R.I., and Breaks, F.W. (comps.), Descriptive Mineral Deposit Models of Metallic and IndustrialDeposit Types and Related Mineral Potential Assessment Criteria, Ontario Geological Survey, Open FileReport 5916, p82-88.

Seedorff, E., Dilles, J.H., Proffett, J.M., Einaudi, M.T., Zurcher, L., Stavast, W.J .A., Johnson, D.A., and Barton,M.D. (2005): Porphyry deposits: characteristics and origin of hypogene features; inHedenquist, J.W.,

Thompson, J.F.H., Goldfarb, R.J., Richards, J.P. (eds.), Economic Geology One Hundredth AnniversaryVolume 1905-2005, Society of Economic Geologists, p251-298.

Sinclair, W.D. (2007): Porphyry deposits; inGoodfellow, W.D. (ed.), Mineral Deposits of Canada, A Synthesis ofMajor Deposit Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods,Geological Association of Canada, Mineral Deposits Division, Special Publication No. 5, p223-244.