Resolving changes in arc magma volatile budgets over Myr timescales leading up to porphyry Cu formation 

2021 ◽  
Author(s):  
Simon Large ◽  
Chetan Nathwani ◽  
Yannick Buret ◽  
Tom Knott ◽  
Jamie Wilkinson
Keyword(s):  
San Francisco ◽  
Volcanic Rocks ◽  
Crustal Thickening ◽  
Ore Formation ◽  
Temporal Shift ◽  
Porphyry Deposit ◽  
Porphyry Cu ◽  
Entire Duration ◽  
Intrusive Activity ◽  
Rock Suite

<p>The crustal-scale magmatic systems of Andean-style arcs produce thick volcanic deposits and abundant plutons that are emplaced into the crust. They can also generate spatially- and temporally-restricted, economically-important porphyry Cu deposits. These deposits are formed at the magmatic-hydrothermal transition and require significant amounts of volatiles and metals to be concentrated in the sub-volcanic environment. Thus, understanding the magmatic and tectonic processes acting within an arc segment and their effect on the volatile budgets of crustal magmas could be essential for identifying the constraining factors controlling the potential of a magmatic system to produce a porphyry deposit.</p><p>In this study we examine the magmatic evolution of the Rio Blanco-Los Bronces district, ~30 km northeast of Santiago, Chile, which is host to the Earth’s largest resource of Cu. Eocene to Early Miocene volcanic rocks were intruded by the Miocene San Francisco Batholith that, in turn, partially hosts intrusions related to the Late Miocene to Early Pliocene Rio Blanco-Los Bronces porphyry deposit cluster. We apply a combination of whole-rock, apatite and zircon geochemistry and zircon geochronology to the intrusive rock suite of the district to provide temporally- constrained geochemical information over the entire duration of batholith assembly and ore formation.</p><p>U-Pb geochronology reveals incremental assembly of the San Francisco Batholith by individual magma batches over >14Myr (~18 – 4 Ma), with ore formation occurring in discrete pulses in the last 3 Myr before cessation of intrusive activity within the district. Progressive changes in the trace element chemistry indicate crustal thickening and deeper magma evolution within the arc segment as a result of the subduction of the Juan Fernandez ridge. A temporal shift to elevated SO<sub>3</sub> and Cl contents is recorded by zircon-hosted apatite inclusions from the intrusions with highest values occurring in porphyry intrusions directly associated with the ore forming events. These data suggest variable volatile budgets of magmas during zircon crystallisation and hint at crustal-scale controls on the porphyry ore-forming potential of an arc segment.</p><p> </p>

Petrochronology resolves the multi-Myr crustal scale magmatic evolution of an arc segment resulting in porphyry copper formation

2020 ◽  
Author(s):  
Simon Large ◽  
Yannick Buret ◽  
Tom Knott ◽  
Jamie Wilkinson
Keyword(s):  
San Francisco ◽  
Subduction Zones ◽  
Porphyry Copper ◽  
Empirical Studies ◽  
Volcanic Rocks ◽  
Geochemical Evolution ◽  
Magma Source ◽  
Magmatic Evolution ◽  
Ore Formation ◽  
The North

<p>The crustal-scale magmatic systems of Andean-style subduction zones produce thick volcanic deposits and abundant plutons emplaced into the upper crust. They can also result in the formation of spatially- and temporally-restricted, economically-important porphyry Cu deposits. Understanding the magmatic and tectonic processes acting within an arc segment, including changes in the fractionating assemblage, subduction angle, chemistry of slab-derived melts or water content, is essential to develop and refine quantitative models for the formation of these deposits. Specific geochemical signatures (e.g. elevated Sr/Y) are associated with magmas that source the metals and volatiles to form porphyry deposits based on empirical studies. However, it is unclear whether this geochemical signature is the result of geologically rapid processes resulting in sudden shifts in magma chemistry or whether they are the result of protracted changes within the crustal-scale magmatic system over extended timescales.</p><p>In this study we examine the magmatic evolution of the Rio Blanco-Los Bronces district, ~30 km northeast of Santiago, Chile, which is host to the Earth’s largest resource of Cu. Eocene to Early Miocene volcanic rocks were intruded by the Miocene San Francisco Batholith that, in turn, partially hosts intrusions related to the Late Miocene to Early Pliocene Rio Blanco-Los Bronces porphyry deposit cluster. We apply a combination of whole-rock and zircon geochemistry, isotopic tracing and LA-ICP-MS U-Pb geochronology to the intrusive rock suite of the district to provide temporally- constrained geochemical information over the entire duration of batholith assembly and ore formation.</p><p>U-Pb geochronology reveals incremental assembly of the San Francisco Batholith by individual magma batches over >13Myr (~17 – 4 Ma), with ore formation occurring in discrete pulses in the last 3 Myr before cessation of intrusive activity within the district. Temporally-resolved whole-rock major element chemistry shows that the progressively-emplaced magmas were not sourced from a common, continuously differentiating, lower crustal magma reservoir. Evolving trace element signatures over the recorded timescale indicate that magmas were sourced from progressively deeper fractional crystallisation reservoir(s) that exhibited increasing water contents. The geochemical evolution recorded over the entire investigated 13 Myr timescale could reflect geodynamic changes linked to the ingression of the subducting Juan Fernandez ridge from the north. However, within this continuous evolution, the most prominent geochemical shifts occur over a much shorter timescale of a few Myr, directly preceding economic ore-formation, implicating an additional mechanism for controlling the metallogenic potential of the magma source.</p><p> </p><p> </p><p> </p>

Mineralogy and textural relationships of ores from the Whalesback Mine, northeastern Newfoundland

1968 ◽  
Vol 5 (6) ◽  
pp. 1387-1395 ◽  
Author(s):  
K. Kanehira ◽  
D. Bachinski
Keyword(s):  
Shear Zone ◽  
Volcanic Rocks ◽  
Sulfide Deposit ◽  
Ore Formation ◽  
Pillow Lavas ◽  
Bay Area ◽  
Internal Reaction ◽  
Sulfide Ore ◽  
Ore Minerals ◽  
Pressure Shadow

The Whalesback Mine is one of many copper deposits associated with Ordovician volcanic rocks in the Notre Dame Bay area, Newfoundland. The deposit consists of veins, pods, and disseminated sulfides localized within a highly chloritized shear zone cutting basaltic pillow lavas. Porphyritic dikes cut the shear zone, sulfide deposit, and the surrounding pillow lavas; all of the rocks, including the sulfide-rich rocks, have been regionally metamorphosed. Ore minerals, in decreasing order of abundance, include pyrite, chalcopyrite, pyrrhotite, sphalerite, mackinawite, pentlandite, magnetite, cubanite, galena, and ilmenite. Marcasite, covellite, and goethite are supergene minerals. Chlorite and quartz are the predominant gangue minerals. Muscovite, carbonates, sphene, albite, and epidote are minor constituents. Banding and streaking of sulfides in massive ores, crushed pyrite, and the local occurrence of pressure-shadow phenomena in the ore are indicative of shearing stress post-dating original sulfide ore formation. Present sulfide assemblages are compatible with relatively low temperatures and are the result of re-equilibration and internal reaction among the sulfides with decreasing temperature.

Lead- and strontium-isotope geochemistry of Paleozoic Sicker Group and Jurassic Bonanza Group volcanic rocks and Island Intrusions, Vancouver Island, British Columbia

1989 ◽  
Vol 26 (5) ◽  
pp. 894-907 ◽  
Author(s):  
Anne Andrew ◽  
Colin I. Godwin
Keyword(s):  
Lead Isotope ◽  
Isotope Geochemistry ◽  
Lead Isotopes ◽  
Volcanic Rocks ◽  
Isotope Ratios ◽  
Ore Deposits ◽  
Island Arc ◽  
Lead Isotope Ratios ◽  
Rock Suite ◽  
Isotope Analyses

Whole-rock and galena lead-isotope analyses have been obtained from the Sicker Group Paleozoic island-arc volcanic package and from a Jurassic island-arc represented by the Bonanza Group volcanics and Island Intrusions. Galena lead-isotope analyses from the volcanogenic ore deposits at the Buttle Lake mining camp in the Sicker Group provide estimates of the initial lead ratios for the Sicker Group. Lead-isotope signatures are uniform within each of the major orebodies, but the Myra orebody is less radiogenic than the older H–W orebody. This has major significance in terms of ore genesis for these important deposits.There are significant differences in isotopic composition between the Sicker Group and Devonian island-arc type rocks in the Shasta district, California, which rules out direct correlations between the rock units of these two areas. Relatively high initial values of 207Pb/204Pb (> 15.56) and 208Pb/204Pb (> 38.00) suggest that large quantities of crustal lead must have been involved in the formation of the Sicker Group volcanic rocks. Thus it is proposed that the trench related to the Paleozoic island arc had a substantial input of continental detritus and may have lain near a continent.The Jurassic island arc is characterized by low 207Pb/204Pb ratios (< 15.59), suggesting a more primitive arc environment than for the Paleozoic arc. Bonanza Group volcanic rocks contain lead that is less radiogenic than lead in the Island Intrusions. Present and initial lead-isotope ratios of both the Bonanza Group volcanics and Island intrusions follow the same trend, supporting the hypothesis that they are comagmatic. Lead isotopes from a galena vein within the Island Copper porphyry deposit plot with the initial ratios for Bonanza Group volcanics and Island Intrusions. This confirms the hypothesis that this mineralization is related to the Jurassic island-arc volcanic event.Initial lead-isotope ratios for the Jurassic rock suite form a linear array on both 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb plots. If interpreted as due to isotopic mixing, the more radiogenic end member has a composition that is lower in 207Pb/204Pb and higher in 206Pb/204Pb than typical upper continental crust. Assimilation of Sicker Group material during the emplacement of the Jurassic arc can explain the mixing trend.

U–Pb geochronology of the Mazinaw terrane, an imbricate segment of the Central Metasedimentary Belt, Grenville Province, Ontario

1995 ◽  
Vol 32 (7) ◽  
pp. 959-976 ◽  
Author(s):  
Fernando Corfu ◽  
R. Michael Easton
Keyword(s):  
Detrital Zircon ◽  
Volcanic Rocks ◽  
Early Period ◽  
Amphibolite Facies ◽  
Crustal Thickening ◽  
Metamorphic Zircon ◽  
Grenville Province ◽  
Marginal Basin ◽  
Lake Formation ◽  
Northern Segment

The Mazinaw terrane, in the Central Metasedimentary Belt of the Grenville Province comprises, volcanic, sedimentary, and plutonic rocks that were intensely folded and faulted, and metamorphosed to as high as upper amphibolite facies. U–Pb geochronology establishes an early period of magmatism and sedimentation at about 1280–1240 Ma, probably in a marginal basin setting, and a multistage rhetamorphic evolution in the period between 1100 and 980 Ma, which was probably related to crustal thickening by imbrication during compression and wedging of the terrane. Some of the earliest magmatism formed calc-alkalic volcanic rocks of Kashwakamak Formation at 1276 ± 2 Ma. An associated sedimentary assemblage was intruded by the Helena trondhjemite stock at 1267 ± 5 Ma. A younger succession, formed between 1250 and 1240 Ma, includes the bimodal volcanic Mazinaw Lake Formation, alaskitic granites of the Norway Lake and Abinger plutons, and a granodioritic gneiss phase of the Cross Lake pluton. These units were covered unconformably by the Flinton Group sometime after 1150 Ma, as defined by published detrital zircon data. A northern segment of the Mazinaw terrane underwent deformation and metamorphism accompanied by the emplacement of granitic pegmatites in the period between 1100 and 1050 Ma. In contrast, metamorphism and deformation occurred significantly later in central domains, as shown by several metamorphic zircon populations grown at about 1040–1030, 1020, and 1010–1000 Ma, by pegmatite emplacement at about 980 Ma, and titanite ages of 1010–960 Ma. Younger rutile ages of about 915 Ma may reflect uplift of the terrane. Some rutile also appears to record the latest Proterozoic faulting and mafic diking related to formation of the Ottawa-Bonnechere graben at about 600 Ma.

Geology and Genesis of the Tuwu Porphyry Cu Deposit, Xinjiang, Northwest China

2020 ◽  
Author(s):  
Yin-Hong Wang ◽  
Fang-Fang Zhang ◽  
Chun-Ji Xue ◽  
Jia-Jun Liu ◽  
Zhao-Chong Zhang ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Growth Curves ◽  
Northwest China ◽  
Hydrothermal Activity ◽  
Positive Trend ◽  
Alteration Zones ◽  
Porphyry Cu ◽  
Potential Applications ◽  
Magmatic Reservoir ◽  
Porphyry Cu Deposit

Abstract The Tuwu porphyry Cu deposit is located in the northern segment of the Jueluotage metallogenic belt in Eastern Tianshan, on the southern margin of the Central Asian orogenic belt, Xinjiang, northwest China. Tuwu is hosted by diorite porphyry and tonalite porphyry intrusions, which intruded volcanic rocks of the Carboniferous Qi’eshan Group. Four stages (I-IV) of hydrothermal activity have been identified. Chalcopyrite is the dominant ore mineral and mainly occurs in vein stages II (quartz-chalcopyrite-pyrite ± sericite ± bornite ± enargite veins with phyllic halos) and III (quartz-molybdenite-chalcopyrite ± pyrite ± chlorite ± epidote veins). Re-Os dating of molybdenite samples yielded an isochron age of 335.6 ± 4.1 Ma (2σ, mean square of weighted deviates = 0.15, n = 8). Silicon, oxygen, and carbon stable isotope compositions of quartz and calcite provide evidence for predominantly magmatic contributions with a late meteoric water component at Tuwu. Chalcopyrite samples from stages I and III record a narrow range of bulk δ34S values between –3.9 and 0.4‰, whereas pyrite samples from stages I to IV show decreasing δ34S values from 1.7 to 0.2‰. Chalcopyrite has 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios similar to those of porphyry intrusions, and Pb isotope data from sulfide samples display a positive trend transecting the growth curves of crustal lead. The ore-forming components (metals and sulfur) were sourced from a mantle-derived magmatic reservoir with some upper crustal components in a subduction-related arc setting. Plagioclase compositions in the porphyry intrusions are consistent with magmatic H2O contents of ~7 wt %. Copper sulfides in the high-grade phyllic alteration zones at Tuwu are characterized by elevated δ65Cu values consistent with deposits from oxidized and hydrous magmatic-hydrothermal fluids, whereas lower δ65Cu values and low copper grades correspond to the potassic alteration zones. Recognition of copper isotope zonation patterns at Tuwu has potential applications in the exploration of porphyry Cu deposits.

scholarly journals From long-lived batholith construction to giant porphyry copper deposit formation: petrological and zircon chemical evolution of the Quellaveco District, Southern Peru

2021 ◽  
Vol 176 (2) ◽  
Author(s):  
Chetan L. Nathwani ◽  
Adam T. Simmons ◽  
Simon J. E. Large ◽  
Jamie J. Wilkinson ◽  
Yannick Buret ◽  
...  
Keyword(s):  
High Pressure ◽  
Porphyry Copper ◽  
Marked Change ◽  
Crustal Thickening ◽  
Deposit Formation ◽  
Nazca Plate ◽  
Southern Peru ◽  
Porphyry Cu ◽  
Lower Crustal ◽  
Crustal Magma

AbstractPorphyry Cu ore deposits are a rare product of arc magmatism that often form spatiotemporal clusters in magmatic arcs. The petrogenetic evolution of igneous rocks that cover the temporal window prior to and during porphyry Cu deposit formation may provide critical insights into magmatic processes that are key in generating these systems. This study documents the magmatic evolution of the Palaeocene–Eocene Yarabamba Batholith, Southern Peru, that was incrementally assembled between ~ 67 and ~ 59 Ma and hosts three, nearly contemporaneous, giant porphyry Cu–Mo deposits that formed at 57–54 Ma (Quellaveco, Toquepala and Cuajone). Whole-rock geochemistry, U–Pb geochronology and zircon trace element chemistry are reported from Yarabamba rocks that span the duration of plutonic activity, and from six porphyry intrusions at Quellaveco that bracket mineralisation. A change in whole-rock chemistry in Yarabamba intrusive rocks to high Sr/Y, high La/Yb and high Eu/Eu* is observed at ~ 60 Ma which is broadly coincident with a change in vector of the converging Nazca plate and the onset of regional compression and crustal thickening during the first stage of the Incaic orogeny. The geochemical changes are interpreted to reflect a deepening of the locus of lower crustal magma evolution in which amphibole ± garnet are stabilised as early and abundant fractionating phases and plagioclase is suppressed. Zircons in these rocks show a marked change towards higher Eu/Eu* (> 0.3) and lower Ti (< 9 ppm) compositions after ~ 60 Ma. Numerical modelling of melt Eu systematics and zircon-melt partitioning indicates that the time series of zircon Eu/Eu* in these rocks can be explained by a transition from shallower, plagioclase-dominated fractionation to high-pressure amphibole-dominated fractionation at deep crustal levels from ~ 60 Ma. Our modelling suggests that any redox effects on zircon Eu/Eu* are subordinate compared to changes in melt composition controlled by the fractionating mineral assemblage. We suggest that growth and intermittent recharge of the lower crustal magma reservoir from ~ 60 Ma produced a significant volume of hydrous and metallogenically fertile residual melt which ascended to the upper crust and eventually generated the three giant porphyry Cu–Mo deposits at Quellaveco, Toquepala and Cuajone from ~ 57 Ma. Our study highlights the importance of high-pressure magma differentiation fostered by strongly compressive tectonic regimes in generating world-class porphyry Cu deposits.

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