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Hope Brook |
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Labrador & Newfoundland, Canada |
| Main commodities:
Au Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The high sulphidation Hope Brook gold deposit is hosted by Neoproterozoic rocks of the Avalon zone in the northern Appalachians on the south-western coast of Newfoundland, Canada.
The ore deposit is hosted by the Neoproterozoic Whittle Hill Sandstone-Third Pond Tuff succession in the hangingwall of the Cinq Cerf Fault zone. The host sequence is in fault contact with the amphibolite facies Neoproterozoic Cinq Cerf Gneiss, is intruded by Ordovician granites (499 Ma), gabbro (495 Ma) and Silurian granites (429 Ma, 419 Ma and 390 Ma) and is overlain by the Silurian (429-422 Ma) La Poile cover sequence of greenschist facies subaerial felsic volcanics and associated epiclastics, separated from the Proterozoic rocks by the Cinq Cerf Fault.
Mineralisation is within highly strained, metamorphosed and intensely altered rocks derived from sandstone, tuffaceous sandstone, greywacke, siltstone, argillite and minor conglomerate-lapilli tuff, which to the NW are in tectonic contact with highly strained felsic vocanics and volcaniclastics of the Silurian La Poile Group. Locally mafic volcaniclastics of the Third Pond tuff and quartz-feldspar porphyries of the Roti Intrusive Suite are intercalated. To the SE a fine grained felsic volcaniclastic up to 70 m thick and 3 km long is found within the sequence.
The hosts to ore are mainly fine grained volcaniclastics (ash flow to crystal tuffs) and/or fine grained intrusives intermixed with coarse grained volcaniclastics. All have been strongly silicified by hydrothermal alteration. A sill-dyke complex up to 400 m thick is found in the hangingwall, composed of: 1). a 200 m wide zone of blue quartz bearing quartz-feldspar porphyries of trondhjemite-tonalite and monzogranite to granodiorite composition; 2). a 150 m wide zone of blue quartz bearing quartz-feldspar porphyries and intermixed mafic intrusions; and 3). 40 to 50 m of mafic to intermediate intrusives, grading to a 150 m thick massive mafic-intermediate intrusive complex to the SE.
The deposit is embraced by a more than 3 km long and 400 m wide (SE thinning) acidic alteration halo, which is bounded to the north by unaltered mylonitised Whittle Sandstone, has a gradational margin to the SE, and is cut to the NE by Devonian granite. This alteration is characterised by 1). an extensive zone of advanced argillic alteration and 2). a buff coloured zone of massive silica alteration.
A late stage, generally tabular, steeply dipping (up to 80 m thick) phase of grey massive silica is spatially coincident with gold mineralisation and is characterised by vuggy quartz. Mineralisation comprises several percent pyrite with lesser chalcopyrite and bornite, some tennantite and local traces of enargite. In addition to the Au and Cu there is anomalous Sb, Bi, Pb and As. Mineralisation is bracketed between 578 and 574 Ma (the age of the Roti Intrusives) and is believed to have been emplaced approximately 150 Ma before the main ductile phase of the adjacent Cinq Cerf Fault zone.
Hope Brook comprises 11.2 Mt @ 4.54 g/t Au for 45 t Au at a cutoff of 2.5 g/t Au, within a global resource amounting to 62 t Au at a 1 g/t Au cutoff, with associated 13 000 t of Cu.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1998.
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.
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Selected References:
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Dube B, Dunning G, Lauziere K 1998 - Geology of the Hope Brook mine, Newfoundland, Canada: a preserved Late Proterozoic high-sulfidation epithermal Gold deposit and its implications for exploration: in Econ. Geol. v 93 pp 405-436
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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