Ruttan, Darrol Lake
Cu Zn Au Ag
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The Ruttan volcanic hosted massive-sulphide (VHMS) CuĐZn deposit is a large, relatively low grade deposit in the Rusty Lake volcanic belt, ~240 km NE of Flin Flon and ~700 km NNW of Winnipeg in northwestern Manitoba, Canada (#Location: 56° 28' 40"N, 99° 39' 19"W).
The deposit originally contained over 82.8 Mt of massive sulphide, of which 55.7 Mt were mined from 1973 to 2002. The grades mined averaged: 1.24% Zn, 1.22% Cu, 12 g/t Ag, 0.48 g/t Au.
The remaining inferred mineral resource at a 1.0% capped copper equiv. cut-off is estimated to be 19.75 million tonnes @ 1.17% Cu and 1.47% Zn (Trevali Mining Corp., 2014).
The Darrol Lake area, ~12 km south of the Ruttan Mine, contains several small, low-grade sulphide deposits.
The Ruttan and Darrol Lake deposits are located in the 1878±3 Ma (U/Pb; Baldwin et al., 1987), 65 x 35 km, Palaeoproterozoic Lynn Lake-Leaf Rapids greenstone belt within the Trans Hudson Orogen. This is part of the more extensive, east-west trending, 1.92 to 1.88 Ga, Palaeoproterozoic La Ronge-Lynn Lake-Partridge Breast-Rusty Lake greenstone belts. The supracrustal rocks within these greenstone belts were folded, faulted and subsequently intruded by larger mafic and felsic plutons. The Rusty Lake greenstone belt is completely surrounded by the paragneiss, orthogneiss and plutonic rocks of the Baldock Batholith. For details of the broader setting of the Rusty Lake greenstone belt see the Flin Flon-Glennie Complex VHMS Deposits record.
Rusty Lake greenstone belt comprises four structurally bound supracrustal blocks, the Karsakuwigamak, Northern, Eastern and Ruttan blocks (Baldwin, 1988). Each of these blocks is separated by major faults that truncate the stratigraphy that defines the respective blocks. The Ruttan and Darrol Lake deposits are hosted within the westernmost Ruttan Block, which consists mainly of submarine mafic volcanic and sedimentary rocks, and is characterised by a northern south-younging and a southern north-younging supracrustal succession (Baldwin, 1988), separated by the composite Corner Lake pluton (Ames, 1996).
The Ruttan deposit is hosted within a thick sequence of felsic to intermediate volcaniclastic rocks predominantly composed of volcanic sandstones, but includes volcaniclastic rocks with recognisable 2 to 30 cm long angular to subrounded rhyolite and basalt fragments (Baldwin, 1988; Ames, 1996). A predominantly mafic rocks occurs to the northwest, separated from the deposit and its altered footwall rocks by the North Wall Shear. This structure is a late, brittle deformation zone that has down-dropped and juxtaposed low-sulphide, weakly altered volcaniclastic rocks to the northwest with rusty-weathered, sulphide-rich, intensely altered and mineralised rocks of the ore zone (Gale et al., 2002).
From north to south, the supracrustal rocks in the immediate mine area are divided into the Mill Pond unit, Mine Sequence, which hosts the ore, and the Powder Magazine unit.
The footwall Mill Pond unit sequence comprises transitional tholeiitic to calc-alkalic basalt and andesite represent, ~500 m down-section from the ore horizon (Barrie et al., 2005). The oldest rocks mapped in the footwall of the deposit are massive, pillowed and volcaniclastic basalt, overlain by the dacitic to rhyolitic Footwall Volcaniclastic rocks and altered Footwall Volcaniclastic rocks (Gale et al., 2002).
Overall, the Mine Sequence has been subdivided into three distinct lithological sections, from north to south. The northern section consists of a 200 to 300 m thick homogeneous sequence of layered, heterolithic, intermediate volcaniclastic rocks, referred to as the 'footwall volcaniclastic rocks'. The middle section, which is ~75 m thick, consists of variably altered volcaniclastic and fragmental volcanic rocks of dacitic and rhyolitic compositions along with associated exhalites. This section hosts several large lenses of massive sulphide mineralisation, which collectively make up the Ruttan deposit. The southern section is up to 100 m thick, and is composed of a distinctive sequence of light grey to white, quartz-phyric, rhyolitic volcaniclastic rocks that have a uranium/lead age of 1883±2 Ma (Maunula and Moreton, 2011).
In the vicinity of the ore lenses, the Mine Sequence, which is steeply dipping, and represent a bimodal volcanic, volcaniclastic and siliciclastic sequence, which in the immediate mine area comprises transitional calc-alkalic to high-silica (tholeiitic), felsic, and intermediate volcanic/volcaniclastic rocks (Ames,1996; Barrie et al., 2005). The footwall volcaniclastic rocks are overlain by the 'Mine Rhyolite', a siliceous volcaniclastic rock that hosts the massive sulphide lenses (Speakman et al., 1982). These rocks are followed by the 'Exhalite Horizon', a >50 m thick package of chemical and clastic sedimentary rocks, 1982), overlain by the Powder Magazine volcaniclastic unit (Speakman et al., 1982; Baldwin, 1988). The 'Exhalite Horizon' comprises at least three units within an up to 200 m thick sequence of altered and mineralised rocks, separated by visually unaltered felsic and intermediate volcanic sandstone and greywacke. The lowermost of these 'exhalite' units is characterised by silicification, coarse-grained chlorite-biotite schist and minor base metals, whereas the uppermost has abundant chert, quartz-sericite schist and minor pyrite (Gale et al., 2002).
The exhalite package appears to overlie the low-grade, main, Cu>>Zn sulphide ore bodies (e.g., the East lens), while the uppermost exhalite band is probably the stratigraphic equivalent of the hanging wall zinc zones, higher-grade, sphalerite-rich, Zn>>Cu lenses that occur in the hanging wall to the main, pyrite-rich, sulphide orebodies (Gale et al., 2002).
Syn-depositional felsic and mafic dykes, sills and apophyses are ubiquitous throughout the Mine Sequence, including within the ore lenses, indicating continued, near-vent magmatism, and volcanism during and after ore formation (Barrie et al., 2005).
The hanging wall rocks are predominantly fine-grained volcaniclastic and siliciclastic rocks, but include polyfragmental agglomerate that contains mafic bombs and scoriaceous felsic fragments (Barrie et al., 2005). In more detail, an ~125 m thick unit of well-bedded, felsic to intermediate volcanic sandstone stratigraphically overlies the exhalite-bearing rocks. Locally, this unit contains <1 m thick beds of mafic and intermediate volcaniclastic rocks, with <1 to 10 cm fragments, and separates the 'exhalite' package and mine sequence from an overlying, ~125 m thick unit of layered quartz- and feldspar-bearing, felsic volcaniclastic rocks. These felsic volcaniclastic rocks, where exposed at surface, are well bedded, contain either mafic and felsic fragments or only felsic fragments, and comprise interlayered felsic sandstone and sandstone-supported breccia. The basal section of the unit is characterised by quartz crystal rich, poorly layered sandstone and grit, passing up into interlayered felsic sandstone, and sandstone with angular 1 to 10 cm fragments, and local quartz-rich and quartz feldspar rich beds. The top of the unit consists of several tens of metres of well-layered felsic sandstone with distinctive 10 to 30 cm thick beds of medium- to coarse-grained, subrounded quartz, capped by finely bedded (mm to cm) felsic siltstone (Gale et al., 2002).
The southern Mine Sequence are in contact with a succession of intercalated greywacke-mudstones and polymictic conglomerates of the Powder Magazine unit. To the west and north of the Ruttan deposit the supracrustal rocks are truncated by the 1852.5±1.2 Ma Brehaut Lake pluton, which is primarily a homogeneous, light grey, medium-grained biotite granodiorite. Contact intrusion breccia zones and dykes emanate from the intrusion. The supracrustal sequence is intruded to the south by the Corner Lake pluton, which in mine area, predominantly comprises dark green, fine-grained hornblende diorite dykes and sills within the mineralization and its host rocks (Maunula and Moreton, 2011).
The altered host rocks have consistent, down-plunge stretching lineations to the SSE that suggest the deposit has been elongated by a factor of ~1.2 to 1.5. Apart from these fabrics, the deposit is relatively undeformed, with syn- and post-depositional faulting in the mine area having only relatively minor offsets up to a few tens of metres. Alteration of footwall rocks within about 200 m of the ore lenses comprises moderate to strong chloritisation, characterised by upper greenschist to lower amphibolite facies assemblages that include cordierite-almandine-andalusite-sillimanite-biotite ±staurolite ±anthophyllite ±talc and local silicification. The proximal hanging wall rocks are characterised by sericite ±gahnite alteration, which is restricted to within approximately 75 m of the uppermost lenses. Other gangue minerals include anhydrite and carbonate minerals (siderite, dolomite, ankerite and calcite), as well as chlorite, sericite, biotite, talc and quartz (Barrie et al., 2005).
The deposit comprises of a series of moderately to steeply dipping (50 to 80°), south-facing and dipping lenses that extend along strike for 1.1 km at the surface and persist to a depth of 1.0 km (Barrie et al., 2005).
There are three principal groups of massive sulphide lenses: i). the East and ii). West lenses, and the iii). B lenses to the far west. The Ruttan lenses are elongated and plunge to the SE at moderate to steep angles (60 to 70°). The long axes of the ore bodies are sub-parallel to mineral and intersection lineations in the host rocks, the hinges of mesoscopic and macroscopic isoclinal F2 folds and the Β-axis of a late network of anatomised D3 shear zones, suggesting structural control (Anderson et al., 2005). The Art's Shear Zone separates the B lenses in the footwall from the West lenses in the hanging wall, whereas the East Shear Zone separates the West lenses in the footwall from the East lenses in the hanging wall. The Art's Shear Zone and the East Shear Zone are sigmoidal structures dipping to the SE at steep to moderate angles, and apparently splaying off the hanging wall of the North Wall Shear Zone. The latter shear zone is steeply SE dipping, and partially envelopes the B lenses in the West Mine. All shear zones are characterised by laterally continuous zones of strongly foliated chlorite-biotite schist that are up to 30 m thick. Dextral shear with a variable component of normal oblique slip is indicated by asymmetric fabrics in the shear zones (Maunula and Moreton, 2011).
The B lens in the West Mine, has a strike length of between 350 and 400 m and is typically 10 to 15 m thick, although, over short distances, both along strike and down dip, it varies from 5 to 40 m. This lens does not outcrop and persists from 170 to 1040 m below surface, with a general plunge of 55 to 65%° to the SSE. The B lens in the Main Mine, is laterally continuous over a strike length of approximately 500 m at surface, with a steep dip to the SSE. It is typically 10 to 15 m thick but locally ranges from 5 to 60 m. Down-dip, the B lens splits into a series of discrete, regularly spaced copper-rich ore shoots that plunge steeply to the SE, with progressively decreasing strike lengths and thicknesses with depth. Within these ore shoots, zones of zinc-rich mineralisation and large dolerite boudins trend at a slight anti-clockwise angle to the strike of the lens. The deepest ore shoot ultimately pinches out at a depth of 370 m below surface (Maunula and Moreton, 2011).
The West group of lenses comprise a complex ore body bounded by the Art's Shear Zone in the footwall, and East Shear Zone in the hanging wall. At surface, these lenses persist over a maximum strike interval of ~350 m, containing intervals of massive sulphides that are as much as 75 m thick, with the thickest accumulations along the western termination of the West lenses, defining a prominent copper-rich shoot plunging at 55 to 65° to the SE, and terminating around 770 m below surface (Maunula and Moreton, 2011).
The East group of lenses, occur over a strike length of approximately 600 m, dipping steeply to moderately to the SE. They extend from surface to >1000 m depth, with a general plunge of 55 to 60° to the SE, and remain open to the east along strike and down plunge to the SE. At the 800 m level, the East lenses are arranged in a tight, roughly U-shaped pattern analogous to that of the West lenses, which is interpreted to be the D3 hinge line of an isoclinal synform overturned to the north-northwest. In the fold hinge, two of the lenses merge to form a copper-rich ore shoot plunging 55° to the SE along the western termination of the East lenses to an ultimate depth of 1050 m (Maunula and Moreton, 2011).
Sulphide mineralisation in the Ruttan deposits is principally composed of pyrite with highly variable, though generally subordinate, proportions of pyrrhotite, chalcopyrite, sphalerite and minor galena with tetrahedrite as the most abundant trace phase. Cu is generally relatively enriched in the stratigraphic base and in the centre of the deposit, whereas Zn is concentrated up-section and at the outer margins. Common gangue minerals include chlorite, biotite, quartz, anthophyllite, magnetite, talc, anhydrite, gypsum, calcite and gahnite in order of decreasing abundance (Maunula and Moreton, 2011). Gahnite is ubiquitous in the chlorite-rich assemblages adjacent to the ore lenses (Barrie et al., 2005).
Three main styles of sulphide mineralisation are recognised in the deposits(after Maunula and Moreton, 2011):
i). Copper-rich massive sulphide, which form the most significant ore bodies in the deposit
ii). zinc-rich layered sulphide, which consists of an irregular body of high-grade zinc mineralisation from the 150 to 600 metre levels, hosted by epidotised biotite schist of the Powder Magazine unit. The mineralisation is composed of approximately 90% coarse-grained, equigranular sphalerite, and 10% combined pyrrhotite, galena, pyrite and chalcopyrite (in order of decreasing relative abundance). Zinc and silver grades in this mineralization are an order of magnitude higher than in the main Ruttan deposit (Anderson et al., 2005).
iii). copper-rich stringer sulphide, which is particularly well developed in the immediate footwall rhyolite of the B lens in the West Mine.
Sulphide mineralisation at Darrol Lake, ~12 km south of the Ruttan Mine, is known in at least four different zones (Dar 1, Dar 2, Dar 3 and Dar 4; Ferreira, 1994) and at several different stratigraphic levels along a strike length of ~10 km where minor pyrrhotite, pyrite, ±sphalerite ±chalcopyrite are encountered (Gale et al., 2002).
At the Dar 2 zone, mineralisation is structurally (and apparently stratigraphically) underlain by rhyolitic volcanic rocks, and overlain by intermediate to mafic volcanosedimentary rocks that are similar to the sandstone portions of the Powder Magazine formation at the Ruttan mine. Rocks in the mineralised zone are dominantly felsic and include felsic sandstone, quartz-sericite schist, quartz-rich intermediate sedimentary rocks and oxide facies iron formation. Pelitic and semipelitic rocks with up to 50% phlogopite are evident within this section. Granitic and pyroxene-rich intrusions are present in both hanging wall and footwall rocks (Gale et al., 2002).
Sections of this description is largely drawn from Maunula, T. and Moreton, C., 2011 - Technical Report on the Former Ruttan Mine, Northern Manitoba, Canada; an NI 43-101 Technical Report prepared for Trevali Mining Corp. by Tetra Tech Wardrop.
The most recent source geological information used to prepare this summary was dated: 2005.
Record last updated: 12/11/2014
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Barrie C T, Taylor C and Ames D E 2005 - Geology and Metal Contents of the Ruttan volcanogenic massive sulfide deposit, northern Manitoba, Canada: in Mineralium Deposita v39 pp 795-812 |
Gale G H, McClenaghan S H and Yaworski R, 2002 - Geology and geochemistry of the Ruttan and Darrol Lake deposits (NTS 63B5), Manitoba: in Report of Activities 2002, Manitoba Geological Survey, Manitoba Industry, Trade and Mines, GS-22, pp. 198–204|
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