Aurora Gold Project - Rorys Knoll, Aleck Hill, Walcott Hill, Mad Kiss
Super Porphyry Cu and Au|
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The Aurora Gold Project is a producing gold mine, which includes the Rory's Knoll, Aleck Hill, Walcott Hill and Mad Kiss zones, that are confined within an ~2 km long corridor, known as the 'Golden Square Mile', located in an uninhabited, forested region of Guyana, ~170 km west of the capital, Georgetown (#Location: 6° 47' 14"N, 59° 44' 41"W).
The deposit cluster is situated in the Palaeoproterozoic Guyana Shield, the northern half of Amazon Craton, comprising a Palaeoproterozoic granite-greenstone terrane, considered to be the extension of the Birimian System of West Africa. The Guyana and West African shields were continuous prior to their separation in the Cretaceous as a result of the opening of the Atlantic Ocean.
The Guiana Shield is largely composed of the Barama-Mazaruni Supergroup, a meta-sedimentary/greenstone terrane intercalated with Archaean-Proterozoic gneisses that are intruded by Trans-Amazonian granites, as well as mafic and ultramafic rocks (McConnell and Williams, 1969). The Barama Group comprises pelitic metasedimentary and metavolcanic rocks, conformably overlain by the Mazaruni Group, which also consists of metasedimentary and metavolcanic rocks. The Mazaruni Group is divided into the Cuyuni and the Haimaraka formations.
The Cuyuni Formation is composed of pebbly sandstone and intraformational conglomerate, intercalated with felsic to mafic volcanic rock. The Haimaraka Formation conformably overlies the Cuyuni Formation and consists of a thick sequence of mudstone, pelite and greywacke, but lacks significant amounts of volcanic rock (McConnell and Williams, 1969).
The Barama-Mazaruni Supergroup formed within a geosynclinal basin locally bordered by an Archaean continental foreland. The ~2 Ga Trans-Amazonian Orogeny, resulted in block faulting, crustal shortening, folding, metamorphism and anatexis of the Barama-Mazaruni Supergroup (Hurley et al., 1967).
The Barama-Mazaruni Supergroup was generally subjected to regional lower to middle greenschist facies metamorphism, although near the contact with some of the larger granitic complexes, it is metamorphosed to upper greenschist to amphibolite facies.
Syn- to late-Tectonic calc-alkaline to intermediate intrusive rocks, collectively known as the Trans-Amazonian Granitoids (Voicu et al., 1999), were emplaced between 2.25 and 1.96 Ga (Gibbs and Barron, 1993), and range from granite to granodiorite, diorite and adamellite in composition. Intrusive rocks proximal to the Aurora Gold Project area include the Proterozoic Iroma-Ranka, Aurora and Katruni medium-grained granodiorite and diorite intrusions, and late-stage basic sills and dykes.
The Aurora deposits are located within a regional NW-striking sub-vertical high strain zone, overprinting metasedimentary and metavolcanic rocks of the Palaeoproterozoic Cuyuni Formation, developed along the northeast margin of an inferred Proterozoic granitic batholith. The distribution of the main lithologies, hydrothermal alteration and strain intensity, are not mappable at surface, due to poor exposure and the deep saprolitic profile, and are deduced from drilling.
The deposit area is divided into a sequence of interbedded metasedimentary and mafic meta-volcanic rocks to the NE, and a suite of mainly mafic meta-volcanic rocks to the SW, and is affected by a series of interconnected 1 to 50 m wide, WNW-ESE to NNW-SSE trending shear zones. A series of 'tonalites' and quartz-feldspar porphyries are located within the zone of shearing.
The Aleck Hill cluster (Aleck Hill and Aleck Hill North) occupies a north-south elongated area that is <200 x 1200 m, on the western margin of the 'Golden Square Mile'. The Rory's Knoll zone (Rory's Knoll, Rory's Knoll East and Walcott Hill East) covers an area that is ~500 x 300 m in area on the northeastern margin of the larger mineralised zone, with mineralisation tapering downward, mainly in the main Rory's Knoll shoot. The Walcott Hill, Mad Kiss West, Mad Kiss and Mad Kiss South zones are distributed, from north to south respectively, over an area that is about 450 m wide and 900 m long between the Aleck Hill and Rory's Knoll clusters.
Shear zones between the Rory's Knoll and Mad Kiss zones strike NW (between 290 and 305°) and dip at 70 to 85°NE. In the Aleck Hill zone, the two main shear zones strike to the SE (~155°) and dip at ~80°SW. These shear zones are characterised by a strong penetrative fabric, locally forming schists in the highest strain zones, and are differentiated as litho-tectonic units, without reference to the protolith.
Steeply-plunging mineral lineations are conspicuous on shear fabrics, suggesting the shear zones have a dominant dip-slip component, whilst the asymmetry of pressure shadows locally developed around competent porphyroblasts suggests SW over NE movement on the shear zones. Strain is strongly partitioned in the deposit zones and rock units adjacent to shear zones are considerably less-strained.
Hydrothermal alteration is spatially related to strain intensity, with the highest strained rocks usually displaying the strongest hydrothermal alteration, e.g., alteration within the shear zones varies between chlorite and muscovite with local strong silica replacement.
The local term 'tonalite' at Rory's Knoll has been shown to be a mafic rock, possibly dioritic in composition, that has undergone intense hydrothermal alteration, including silicification. It is unclear if this rock unit is intrusive. It is a competent lithology in which auriferous quartz-ankerite veins represent dilational sites developed during active deformation and fracturing. The auriferous veins of Walcott Hill, Walcott Hill East and Rory's Knoll East are hosted within a similar rock type.
The quartz and feldspar porphyry dykes in the Mad Kiss zone, locally referred to as a 'quartz-phyric felsic intrusions', also represent a competent lithology in which auriferous veins formed in response to dilation. Metasedimentary rocks comprise turbiditic laminated to thickly-bedded argillite and greywacke. The interbedded sequence of metasedimentary and mafic metavolcanic rocks consists primarily of metasedimentary rock with mafic metavolcanic rock subunits. Mafic metavolcanic rocks form the SW contact of Rory's Knoll, the host rock of the Aleck Hill deposit, and the Mad Kiss Quartz and Feldspar Porphyry. Some mafic rocks are very strongly magnetic, especially in the Mad Kiss and Walcott Hill areas, and are particularly apparent on aeromagnetic data.
Gold mineralisation in the 'Golden Square Mile' is controlled by a series of NW-SE trending shear zones, orientated sub parallel to the dominant structural trend found throughout the Aurora Project area. These shear zones contain a steep NW-SE trending foliation that formed during NE-SW shortening.
The gold mineralisation is chiefly associated with quartz-ankerite veins containing minor pyrite and associated hydrothermal alteration. The auriferous veins form weak to moderate stockworks, preferentially in competent lithologies outside the most intensely deformed and altered segments of the shear zones. The auriferous veins have undergone minor post formation deformation. The geometry of the auriferous stockworks is controlled by the geometry of the competent lithologies and the geometry of shear zones, or a combination of both.
The Aurora Gold Project is divided into four major gold mineralisation zones Rory's Knoll (including Walcott Hill East), Aleck Hill (including Aleck Hill North), Walcott Hill, and Mad Kiss (including Mad Kiss West), and may be summarised as follows:
Rory's Knoll and Walcott Hill East
Gold mineralisation at Rory's Knoll extends for ~250 m along a 300° trend and plunges at ~80°NW. It is ~100 m thick at the widest point and has been intersected by drilling to a depth of ~1600 m below the surface.
The auriferous veins are developed within a distinctive, highly altered porphyritic diorite unit (locally known as 'tonalite'), which is intensely carbonate and possibly albite altered. A well-developed shear zone is located along the south-western contact of the Rory's Knoll 'tonalite', typified by strongly foliated muscovite schists with an associated down-dip stretching lineation. Abundant gold-rich quartz-ankerite veins occur in the 'tonalite' near the sheared contact, with vein density increasing towards the sheared contact. The steep northerly plunge at Rory's Knoll is interpreted to represent the intersection between a sub-vertical NW trending shear zone and the steeply dipping, possibly west trending, competent altered 'tonalite'.
Gold mineralisation persists to the west into Walcott Hill East, which is adjacent to and located ~60 m SW of the main Rory's Knoll shoot. Walcott Hill East is ~50 m long and ~15 m wide. It comprises a zone of auriferous weak quartz-ankerite stockwork veining enveloped by intense 'grey' silica alteration at the contact between a felsic and a mafic rock. This veining is preferentially developed in a distinct competent silica-rich lithological unit at the contact with muscovite schists to the east, where veining is absent. The rheology contrast between silica-rich rock and muscovite schist is interpreted to control the formation of auriferous quartz-carbonate veins at Walcott Hill East. Similar to Rory's Knoll, it may be related to the intersection of NW-trending shear zones and favorable host rocks trending at high angle to the shear zones.
The main Aleck Hill mineralisation is centred ~1000 m west to WSW of the Rory's Knoll Zone, and occurs in two zones, Aleck Hill and Aleck Hill North. The gold zones of the main Aleck Hill deposit strike at 150° and dip sub vertically, and can be up to 20 m wide. The deposit extends for ~1000 m along strike, with higher-grade material and old underground workings persisting for ~400 m down dip, although mineralisation has been intersected to depths of ~600 m below surface.
Aleck Hill North is ~500 m NNW of Aleck Hill, and extends for ~250 m along strike, is steeply dipping, and has a maximum thickness of ~35 m. The zone is truncated at its northern and southern end, but continues to depth.
The gold mineralisation at Aleck Hill occurs as auriferous quartz-carbonate veins developed inside discrete shear zone that are sub-parallel to the NW-trending regional foliation, and follow lithological contacts within moderately strained, weakly altered mafic volcanic rocks. This auriferous quartz-carbonate veining formed late relative to the development of the foliation. Quartz-carbonate stockwork veins occur with both flat veins normal to foliation and high angle veins at low angle to foliation. At Aleck Hill, characteristic 'pink' quartz alteration is associated with the quartz-ankerite veins occurring in veins, vein selvages and pervasive replacement in strong stockwork zones. At Aleck Hill North, high strain and alteration zones developed at gradational contacts between diorite and mafic volcanic rocks.
This deposit is ~500 m SW of the Rory's Knoll Zone. Gold mineralisation occurs as gold-bearing quartz veins that are up to 0.6 m thick, striking at 320° and dipping sub-vertically, with each persisting for ~35 m along strike. This zone has been intersected by drilling to a depth of ~650 m below surface.
The main Mad Kiss Zone is ~750 m SSW of Rory's Knoll. Quartz-carbonate veining occurs inside a sheared quartz-feldspar porphyry dyke enclosed in foliated muscovite-rich rock. The gold-bearing stockwork system trends at ~150° and dips steeply north and south, associated with both the hanging wall and footwall contacts of the porphyry dyke, which is up to 150 m wide. Gold mineralisation trends at 250°, dips 70° N and has been intersected in drilling to a depth of ~700 m below surface. Individual auriferous veins are 2 to 5 cm thick, and occur both parallel and normal to the regional foliation. The lower contact of the quartz feldspar porphyry dyke is sometimes marked by a thick quartz-carbonate vein with variable gold grades. There is no veining in the enclosing muscovite-rich rock.
The Mad Kiss West Zone is located 200 m NW of the main Mad Kiss Zone, and contains gold mineralisation striking between 250 and 290° and dipping sub-vertically. A strong alteration zone is developed at the contact between unaltered strongly magnetic mafic volcanic rock and unaltered diorite. Quartz-ankerite gold veins occur near the upper (hanging wall) contact as a stockwork developed in strongly altered dioritic rock of mostly unstrained veins.
Available observations suggests Mad Kiss, and possibly Mad Kiss West, are controlled by the high angle intersection of NW-trending shear zones with favourable host rocks, and possibly have an overall plunge of the auriferous zones similar to that of the Rory's Knoll Zone.
Published NI 43-101 compliant mineral resources at Sept 30, 2015 (Wilson et al., 2016; by SRK for AGM Inc.,) were:
Open pit - cutoff 0.3 and 0.4 g/t Au for saprolite and primary ore respectively.
Measured resource (all at Rory's Knoll)
saprolite - 0.1 Mt @ 3.63 g/t Au, primary - 5.62 Mt @ 3.23 g/t Au, TOTAL - 5.72 Mt @ 3.24 g/t Au.
Indicated resource (at Aleck Hill, Rory's Knoll, Wallcott Hill, Mad Kiss and miscellaneous saprolites)
saprolite - 5.28 Mt @ 1.89 g/t Au, primary - 21.51 Mt @ 2.66 g/t Au, TOTAL - 26.78 Mt @ 2.51 g/t Au.
Inferred resource (at Aleck Hill, Rory's Knoll, Wallcott Hill, Mad Kiss and miscellaneous saprolites)
saprolite - 2.84 Mt @ 1.10 g/t Au, primary - 2.23 Mt @ 2.11 g/t Au, TOTAL - 5.08 Mt @ 1.54 g/t Au.
Underground - cut-off 1.8 g/t Au - all is primary ore.
Indicated resource (at Aleck Hill, Rory's Knoll, Wallcott Hill and Mad Kiss)
primary - 30.06 Mt @ 3.91 g/t Au.
Inferred resource (at Aleck Hill, Rory's Knoll, Wallcott Hill and Mad Kiss)
primary - 11.81 Mt @ 4.12 g/t Au.
Combined open pit and underground by deposit and ore type
saprolite - 0.10 Mt @ 3.63 g/t Au, primary - 5.62 Mt @ 3.23 g/t Au, TOTAL - 5.72 Mt @ 3.24 g/t Au
saprolite - 0.28 Mt @ 2.97 g/t Au, primary - 33.42 Mt @ 3.60 g/t Au, total - 33.70 Mt @ 3.59 g/t Au.
saprolite - 2.10 Mt @ 2.54 g/t Au, primary - 14.30 Mt @ 2.81 g/t Au, total - 16.39 Mt @ 2.77 g/t Au.
saprolite - 0.26 Mt @ 2.03 g/t Au, primary - 3.06 Mt @ 4.09 g/t Au, total - 3.32 Mt @ 3.93 g/t Au.
saprolite - 0.05 Mt @ 2.37 g/t Au, primary - 0.80 Mt @ 2.22 g/t Au, total - 0.85 Mt @ 2.23 g/t Au.
saprolite - 2.59 Mt @ 1.13 g/t Au.
TOTAL measured + indicated resource
saprolite - 5.38 Mt @ 1.92 g/t Au, primary - 57.19 Mt @ 3.37 g/t Au, TOTAL - 62.57 Mt @ 3.25 g/t Au.
saprolite - 0.03 Mt @ 2.28 g/t Au, primary - 9.66 Mt @ 4.20 g/t Au, total - 9.69 Mt @ 4.19 g/t Au.
saprolite - 0.28 Mt @ 1.55 g/t Au, primary - 2.96 Mt @ 2.83 g/t Au, total - 3.24 Mt @ 2.72 g/t Au.
saprolite - 0.21 Mt @ 2.21 g/t Au, primary - 1.24 Mt @ 3.23 g/t Au, total - 1.45 Mt @ 3.08 g/t Au.
saprolite - 0.01 Mt @ 2.78 g/t Au, primary - 0.18 Mt @ 2.33 g/t Au, total - 0.20 Mt @ 2.35 g/t Au.
saprolite - 2.31 Mt @ 0.93 g/t Au.
TOTAL inferred resource
saprolite - 2.84 Mt @ 1.10 g/t Au, primary - 14.05 Mt @ 3.80 g/t Au, TOTAL - 16.89 Mt @ 3.34 g/t Au.
TOTAL measured + indicated + inferred resource - 79.64 Mt @ 3.26 g/t Au.
This summary is drawn from "Wilson, S.E., Pennstrom, W.J., Brechtel, C.E., Cole, G., Telford, M. and DeLong, R., 2016 - Ni 43-101 Technical Report, 2015, Updated Feasibility Study for the Aurora Gold Project, Guyana; prepared for AGM Inc., by Metal Mining Consultants Inc. and SRK Consulting (Canada), Inc., 299p."
The most recent source geological information used to prepare this summary was dated: 2015.
Record last updated: 2/2/2016
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
John, D.A., du Bray, E.A., Henry, C.D. and Vikre, P.G., 2015 - Cenozoic Magmatism and Epithermal Gold-Silver Deposits of the Southern Ancestral Cascade Arc, Western Nevada and Eastern California: in New Concepts and Discoveries, Geological Society of Nevada, 2015 Symposium, Reno/Sparks, Nevada, May 14 to 24, 2015, Symposium Proceedings, pp. 611-645.|
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