20 research outputs found
Geochemistry, geochronology, and fluid inclusion study of the Late Cretaceous Newton epithermal gold deposit, British Columbia
Newton is an intermediate-sulfidation epithermal gold deposit related to Late Cretaceous continental arc magmatism in south-central British Columbia. Disseminated gold mineralization occurs in quartz-sericite-altered Late Cretaceous felsic volcanic rocks, and feldspar-quartz-hornblende porphyry and quartz-feldspar porphyry intrusions. The mineralization can be divided into 3 stages: (1) disseminated pyrite with microscopic gold inclusions, and sparse quartz-pyrite ± molybdenite veins; (2) disseminated marcasite with microscopic gold inclusions and minor base metal-sulfides; and (3) polymetallic veins of pyrite-chalcopyrite-sphalerite-arsenopyrite.
Re-Os dating of molybdenite from a stage 1 vein yielded an age of 72.1 ± 0.3 Ma (McClenaghan 2013). The age of the host rocks has been constrained by U-Pb dating of zircon: Late Cretaceous felsic volcanic rocks: 72.1 ± 0.6 Ma (Amarc Resources Ltd., unpublished data, reported in McClenaghan 2013); feldspar-quartz-hornblende porphyry: 72.1 ± 0.5 Ma; quartz-feldspar porphyry: 70.9 ± 0.5 Ma (Amarc Resources Ltd., unpublished data, reported in McClenaghan 2013). The mineralized rocks are intruded by a barren diorite, with an age of 69.3 ± 0.4 Ma.
Fluid inclusions in quartzâpyrite ± molybdenite ± gold veins yielded an average homogenization temperature of 313° ± 51°C (n = 82) and salinity of 4.8 ± 0.9 wt.% NaCl equiv. (n = 46), suggesting that a relatively hot and saline fluid likely of magmatic origin was responsible for the first stage of mineralization. Some evidence for boiling was also observed in the veins. However, the bulk of the gold mineralization occurs as disseminations in the wallrocks, suggesting that wallrock reactions were the main control on ore deposition.
Keywords: Newton, Intermediate-sulfidation, Epithermal, Gold, British ColumbiaThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Peri-Gondwanan terrane interactions recorded in the CambrianâOrdovician detrital zircon geochronology of North Wales
Precambrian to Ordovician sedimentary basins of Wales display contrasting histories across major NE-striking fault systems. Northeast of the Menai Strait Fault System the Monian Supergroup is a deformed succession of mainly metaclastic rocks. Within the fault system the Arfon Basin contains sandstone and slate overlying Neoproterozoic volcanic rocks. South of the fault system, in the Harlech Dome of the Welsh Basin, a distinctive succession of clastic rocks has been correlated with those of the Meguma Terrane in the northern Appalachian orogen, together comprising the domain Megumia. A detrital zircon analysis from Cambrian sandstone in the Harlech Dome is consistent with this correlation. However, the Early Ordovician Dol-cyn-afon Formation higher in the succession and the overlying Late Ordovician Conway Castle Sandstone show a more diverse provenance, consistent with derivation from the Monian Supergroup. Cambrian sandstone from the Llanberis Slates Formation in the Arfon Basin shows a distinct provenance dominated by a Neoproterozoic source. None of the samples analyzed contains Laurentian detritus. These results suggest that the Welsh Basin was juxtaposed with the Monian Supergroup and its Precambrian substrate along the Menai Strait Fault System by the Tremadocian, and indicate that the Iapetus Ocean remained open at least until the Silurian. The Cambrian detrital zircon record from the Arfon Basin does not show clear similarity to the Monian Supergroup, nor to the Welsh Basin and adjacent Midland Platform, indicating that the basin was isolated from these sedimentary sources within the fault system. The juxtaposition of these terranes probably took place during strike-slip to transpressional tectonism close to the northern margin of Gondwana during the Early Ordovician
Stratigraphy, provenance and tectonic setting of the Lumsden Dam and Bluestone Quarry formations (Lower Ordovician), Halifax Group, Nova Scotia, Canada
Cambrian to Ordovician metamorphosed clastic sedimentary rocks of the Meguma terrane have no correlatives elsewhere in Atlantic Canada but are similar to successions in North Wales. In the Meguma terrane, the Cambrian Goldenville Group, dominated by sandstone, is overlain by the Halifax Group, consisting mainly of fine-grained slate and siltstone. Within the Halifax Group widespread Furongian black slate units are overlain by greyer units with rare Early Ordovician fossils, assigned to the laterally equivalent Bear River, Feltzen, Bluestone Quarry, Lumsden Dam and Glen Brook formations. The type section of the Bluestone Quarry Formation, here defined, is on Halifax Peninsula, where four constituent members are recognized; the type section of the Lumsden Dam Formation is here defined in the Lumsden Dam region near Wolfville. Detrital zircons extracted from a sample of the Lumsden Dam Formation show a range of ages similar to those displayed by the underlying Goldenville Group, including abundant Neoproterozoic zircon representing Avalonian or Pan-African sources, and a prominent group of peaks between 1.95 and 2.2 Ga, probably representing sources in West Africa. A sample from the Glen Brook Formation east of Halifax shows a similar distribution. In contrast to the correlative Welsh successions, no influx of Mesoproterozoic zircon is seen in Early Ordovician samples, suggesting that, if the two basins were in close proximity in the Cambrian, they had diverged by the Early Ordovician, possibly as a result of strike-slip motion along the margin of Gondwana
Geology and age of the Morrison porphyry Cu-Au-Mo deposit, Babine Lake area, British Columbia
The Morrison porphyry Cu-Au-Mo deposit is genetically and spatially related to Eocene plagioclase-hornblende-biotite porphyry intrusions. One porphyry intrusion yielded a U-Pb age of 52.54 ± 1.05 Ma. Mineralization occurs in three stages: (1) vein-type and disseminated chalcopyrite and minor bornite (associated with potassic alteration and gold mineralization); (2) vein-type molybdenite (associated with weak phyllic alteration); and (3) polymetallic sulfide-carbonate veins (dolomite ± quartz-sphalerite-galena-arsenopyrite-chalcopyrite, associated with weak sericite-carbonate alteration). Re-Os dating of molybdenite yielded ages of 52.54 ± 0.22 and 53.06 ± 0.22 Ma, similar to the age of the host porphyry intrusion.
Stage 1 vein fluids were predominantly magmatic origin: Th = 400° to 526°C; salinity = 39.8 to 47.8 wt.% NaCl equiv.; ÎŽ18Ofluid = 3.7â°â6.3â°; disseminated chalcopyriteâpyrite ÎŽ34SCDT = 0.2â° and â0.8â° (CDT, Canyon Diablo Troilite). Stage 2 fluids were a mixture of magmatic and meteoric water: Th = 320â421 °C; salinity = 37.0â43.1 wt.% NaCl equiv.; ÎŽ18Ofluid values range from 0.3â° to 3.4â°; molybdenite and pyrite ÎŽ34SCDT = â2.1â° and â1.2â°. Stage 3 fluids were predominantly of meteoric water origin: Th = 163â218 °C; salinity = 3.1â3.9 wt.% NaCl equiv.; ÎŽ18Ofluid = â2.3â° to 3.9â° for early vein quartz, and 1.1â° to 6.1â° for late vein dolomite; sphalerite and pyrite ÎŽ34SCDT = â7.1â° to â5.6â°. Morrison is interpreted to be a typical porphyry CuâAuâMo deposit related to a calc-alkaline to a high-K calc-alkaline diorite to granodiorite intrusive suite, generated in a continental arc in response to early Eocene subduction of the KulaâFarallon plate beneath North America.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Evaluating the Age Distribution of Exposed Crust in the Acasta Gneiss Complex Using Detrital Zircons in Pleistocene Eskers
Abstract The Acasta Gneiss Complex (AGC) is a âŒ2,400 km2 HadeanâMesoarchean terrane that contains the oldest known zirconâbearing rocks on Earth. Despite its importance for early Earth geology, only a small fraction (âŒ50 km2) of the AGC has been mapped in detail. We use detrital zircon grains from late Pleistocene eskers that transect the Complex to approximate the lateral extent and relative proportions of diverseâaged ancient rock units within the vast, littleâstudied parts of the AGC. The esker sediment was derived from glacially eroded bedrock and therefore zircon grains can serve as a proxy for the ages of exposed bedrock in the study area. UâPb dates on âŒ2400 detrital zircons from coarse and fine grainâsize fractions along the esker transect yield age distributions that coincide with ages of regionally mapped AGC bedrock, the adjacent Wopmay Orogen, and granitoids of the Slave craton. Based on detrital zircon age distributions and new reconnaissanceâscale mapping, we infer that 3.37 Ga granitoids are a volumetrically significant component of the unmapped AGC. Esker zircons older than 3.7 Ga are present in most esker samples but at low abundance, which suggests that Eoarchean and Hadean rocks are a volumetrically subordinate component of the AGC. However, the data also suggest that unmapped rocks at least as old as 3.95 Ga are present toward the inferred eastern limit of the AGC, a location where Eoarchean rocks have not been recognized previously
Ganderia-Laurentia collision in the Caledonides of Great Britain and Ireland
During terrane convergence, an influx of clastic sediment from an upper plate onto a lower plate is an early indication of terrane juxtaposition. In the Caledonides of Great Britain and Ireland, units accreted to Laurentia during the early Palaeozoic Era include peri-Gondwanan terrane assemblages that earlier separated from West Gondwana. However, the Southern Uplands Terrane contains detrital zircon populations apparently derived entirely from Laurentia, characterized by a large, asymmetric Mesoproterozoic peak and a scarcity of zircon at 600 Ma and 2.1 Ga. In contrast, Cambrian and Ordovician rocks from the Lake District and the Leinster Massif of Ireland show abundant grains with these ages, together with a range of Mesoproterozoic zircon. These characteristics are shared with the Monian terrane of Anglesey and with Ganderia in the Appalachians, indicating probable derivation from Amazonia in West Gondwana. Silurian sandstones from the Lake District show an influx of Laurentia-derived zircon, and lack the peri-Gondwanan signal. This indicates that in the Caledonides, Ganderia was not accreted to the Laurentian margin until c. 430 Ma, in contrast to the Ordovician accretion of Ganderian fragments recorded in the Appalachians, suggesting that the configuration of the closing Iapetus Ocean varied significantly along the strike of the orogen
Temporal evolution of the giant Salobo IOCG deposit, CarajĂĄs Province (Brazil): constraints from paragenesis of hydrothermal alteration and U-Pb geochronology
FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOThe giant Salobo copper-gold deposit is located in the CarajĂĄs Province, Amazon Craton. Detailed drill core description, petrographical studies, and U-Pb SHRIMP IIe and LA-ICP-MS geochronology unravel its evolution regarding the host rocks, hydrothermal alteration and mineralization. Within the Cinzento Shear Zone, the deposit is hosted by orthogneisses of the Mesoarchean Xingu Complex (2950 ± 25 and 2857 ± 6.7 Ma) and of the Neoarchean IgarapĂ© Gelado suite (2763 ± 4.4 Ma), which are crosscut by the Old Salobo granite. Remnants of the IgarapĂ© Salobo metavolcanic-sedimentary sequence are represented by a quartz mylonite with detrital zircon populations (ca. 3.1â3.0, 2.95, 2.86, and 2.74 Ga). High-temperature calcic-sodic hydrothermal alteration (hastingsite-actinolite) was followed by silicification, iron-enrichment (almandine-grunerite-magnetite), tourmaline formation, potassic alteration with biotite, copper-gold ore formation, and later Fe-rich hydrated silicate alteration. Myrmekitic bornite-chalcocite and magnetite comprise the bulk of copper-gold ore. All these alteration assemblages have been overprinted by post-ore hematite-bearing potassic and propylitic alteration, which is also recognized in the Old Salobo granite. In the central zone of the deposit the mylonitized IgarapĂ© Gelado suite rocks yield an age of 2701 ± 30 Ma. Zircon ages of 2547 ± 5.3 and 2535 ± 8.4 Ma were obtained for the Old Salobo granite and for the high-grade copper ore, respectively. A U-Pb LA-ICP-MS monazite age (2452 ± 14 Ma) from the copper-gold ore indicates hydrothermal activity and overprinting in the Siderian. Therefore, a protracted tectono-thermal event due to the reactivation of the Cinzento Shear Zone is proposed for the evolution of the Salobo deposit525709732FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOFAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICO573733/2008-22009/18371-02013/25659-5481969/2013-6308365/2014-
Timing of multiple hydrothermal events in the iron oxideâcopperâgold deposits of the Southern Copper Belt, CarajĂĄs Province, Brazil
CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOFAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOThe Southern Copper Belt, Carajas Province, Brazil, hosts several iron oxide-copper-gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U-Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW-ESE shear zones. They encompass Mesoarchean (3.08-2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite-scapolite, biotite-scapolite-tourmaline-magnetite alteration, and proximal potassium feldspar, chlorite-epidote and chalcopyrite formation. U-Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re-Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72-2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90-1.88-Ga ore formation in the Sossego-Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajas Basin formation, the main episode of IOCG genesis (2.72-2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarap, Bahia-Alemo deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajas Province with a single extensive hydrothermal system is precluded.The Southern Copper Belt, Carajas Province, Brazil, hosts several iron oxide-copper-gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U-Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW-ESE shear zones. They encompass Mesoarchean (3.08-2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite-scapolite, biotite-scapolite-tourmaline-magnetite alteration, and proximal potassium feldspar, chlorite-epidote and chalcopyrite formation. U-Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re-Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72-2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90-1.88-Ga ore formation in the Sossego-Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajas Basin formation, the main episode of IOCG genesis (2.72-2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarap, Bahia-Alemo deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajas Province with a single extensive hydrothermal system is precluded505517546CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOFAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOFAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPq [555065/2006-5, 472549/2009-0, 481969/2013-6]FAPESP [03/11163-603/01159-1, 2009/18371-0]FAPESP [573733/2008-2]FAPESP [01/2010 ICAAF 053/2011]555065/2006-5; 472549/2009-0; 481969/2013-603/11163-603/01159-1; 573733/2008-2; 01/2010 ICAAF 053/2011; 2009/18371-
GanderiaâLaurentia collision in the Caledonides of Great Britain and Ireland
<p>During terrane convergence, an influx of clastic sediment from an upper plate onto a lower plate is an early indication of
terrane juxtaposition. In the Caledonides of Great Britain and Ireland, units accreted to Laurentia during the early Palaeozoic
Era include peri-Gondwanan terrane assemblages that earlier separated from West Gondwana. However, the Southern Uplands Terrane
contains detrital zircon populations apparently derived entirely from Laurentia, characterized by a large, asymmetric Mesoproterozoic
peak and a scarcity of zircon at 600 Ma and 2.1 Ga. In contrast, Cambrian and Ordovician rocks from the Lake District and
the Leinster Massif of Ireland show abundant grains with these ages, together with a range of Mesoproterozoic zircon. These
characteristics are shared with the Monian terrane of Anglesey and with Ganderia in the Appalachians, indicating probable
derivation from Amazonia in West Gondwana. Silurian sandstones from the Lake District show an influx of Laurentia-derived
zircon, and lack the peri-Gondwanan signal. This indicates that in the Caledonides, Ganderia was not accreted to the Laurentian
margin until <em>c</em>. 430 Ma, in contrast to the Ordovician accretion of Ganderian fragments recorded in the Appalachians, suggesting that the
configuration of the closing Iapetus Ocean varied significantly along the strike of the orogen.
</p