Copper and iron isotopic signatures in sulfide and silicate minerals are important genetic indicators in magmatic sulfide deposits. Kalatongke is a large‐scale magmatic Cu‐Ni sulfide deposit in the ...Central Asian Orogenic Belt, and one that experienced multiple stages of magmatism and contamination. It is an ideal deposit in which to study Cu‐Fe isotopic fractionation during multiple stages of magmatism and sulfide mineralization processes. The Kalatongke sulfide orebodies are hosted by three small mafic intrusions in which pyroxene and sulfides (pyrrhotite, pentlandite, and chalcopyrite) are the most common Fe‐rich minerals, and chalcopyrite is the dominant Cu‐rich mineral. Sulfide liquid and silicate melt ▵56FeSul‐Sil (0.03–0.19‰) and ▵65CuCcp‐Sil (−0.78–0.74‰) values are indicative of non‐equilibrium fractionation. Most of the Cu isotope compositions in the sulfide ores at Kalatongke can be modeled as subduction‐ metasomatized, oxidized mantle source‐derived silicate melt (initial δ57Fe = 0.15‰, δ65Cu = −0.07‰) that underwent lower crustal contamination, and then reacted with silicate melt, having an R factor of 100–1,000. Rapid silicate melt and sulfide liquid Fe isotope exchange and re‐equilibration between chalcopyrite and pyrrhotite in the massive ores is reflected in the similarity of their δ56Fe values. Sulfide in disseminated ores shows a range of Fe isotope ratios, influenced by the proportions of monosulfide solid solution (MSS) and intermediate solid solution (ISS) formed. Copper isotopes can be utilized to characterize crustal contamination and silicate melt‐sulfide liquid interaction, while the Fe isotope ratios of sulfide minerals record sulfide liquid segregation and evolution in magmatic sulfide deposits.
Key Points
Sulfide δ65Cu and δ56Fe signatures reflect crustal contamination, sulfide and silicate melt reactions, and sulfide liquid segregation
Copper isotopes can record the source and crustal contamination, sulfide liquid and silicate melt reaction, and sulfide segregation
Various range of sulfide minerals Fe isotopes influenced by the segregation of MSS and ISS and their ratios
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Significant changes in tectonic style and climate occurred from the late Archaean to early Proterozoic when continental growth and emergence provided opportunities for photosynthetic life to ...proliferate by the initiation of the Great Oxidation Event (GOE). In this study, we report a Neoarchaean passive-margin-type sequence (2560-2500 million years ago) from the Precambrian basement of China that formed in an accretionary orogen. Tectonostratigraphic and detrital zircon analysis reveal that thermal subsidence on the backside of a recently amalgamated oceanic archipelago created a quiet, shallow water environment, marked by deposition of carbonates, shales, and shallow water sediments, likely hosts to early photosynthetic microbes. Distinct from the traditional understanding of passive margins generated by continental rifting, post-collisional subsidence of archipelago margins represents a novel stable niche, signalling initial continental maturity and foreshadowing great changes at the Archaean-Proterozoic boundary.
Granitoid-hosted mineral deposits are major global sources of a number of economically important metals. The fundamental controls on magma metal fertility are tectonic setting, the nature of source ...rocks, and magma differentiation. A clearer understanding of these petrogenetic processes has been forged through the accessory mineral zircon, which has considerable potential in metallogenic studies. We present an integrated zircon isotope (U-Pb, Lu-Hf, O) and trace element dataset from the paired Cu-Au (copper) and Sn-W (tin) magmatic belts in Myanmar. Copper arc zircons have juvenile εHf (+7.6 to +11.5) and mantle-like δ
O (5.2-5.5‰), whereas tin belt zircons have low εHf (-7 to -13) and heavier δ
O (6.2-7.7‰). Variations in zircon Hf and U/Yb reaffirm that tin belt magmas contain greater crustal contributions than copper arc rocks. Links between whole-rock Rb/Sr and zircon Eu/Eu* highlight that the latter can monitor magma fractionation in these systems. Zircon Ce/Ce* and Eu/Eu* are sensitive to redox and fractionation respectively, and here are used to evaluate zircon sensitivity to the metallogenic affinity of their host rock. Critical contents of Sn in granitic magmas, which may be required for the development of economic tin deposits, are marked by zircon Eu/Eu* values of ca. ≤0.08.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
To further our knowledge of ore genesis in one of Australia's preeminent ore districts, we have completed a comprehensive geochemical study of ore-related porphyritic intrusions from the Archaean ...Kanowna Belle and Sunrise Dam gold deposits (both >10 Moz), Eastern Goldfields, Western Australia. Zircon samples (including samples from the newly developed Velvet mine) with ages ranging from 2.8 to 2.2 Ga, were investigated for O-OH isotopic signatures, trace element abundance, and U-Th-Pb compositions to elucidate the nature of the magmatic source and ore-related fluid. These intrusions have similarly high Sr/Y and La/Yb ratios to adakites from the Aleutian and Cook Islands, but lower Mg# values and higher K2O contents, suggesting they were derived from partial melts in a thickened crust. The modern analogs are post-collisional, high-Sr/Y granitoid porphyries in southern Tibet. Magmatic zircons have intermediate δ18O values (+5 ppm to +6.3 ppm), and estimated magmatic crystallization temperatures (Ti-in-zircon) in between 660-760°C. They are interpreted as having crystallized from positive δ18O magmas during water-fluxed melting of juvenile lower crust. Hydrothermal fluid modified zircons are texturally indistinguishable from magmatic zircons, but their trace element, OH, and isotopic compositions are distinct. The involvement of hydrothermal fluid in zircon growth is evidenced by a negative correlation between OH content and δ18O. In addition, the studied hydrothermal fluid modified zircons are characterized by high La contents, flat rare earth element patterns, weak Ce anomalies, and high Eu/Eu* ratios, suggesting they were related to a high-temperature, Zr-saturated, high-Eu, Cl-rich, and low-pH hydrothermal fluid. Such fluids are common in eastern Yilgarn gold camps.
The Singhbhum Craton and supracrustal provinces in eastern India are one of a few Precambrian terranes that record protracted sedimentation and magmatism spanning the Paleoarchean to Neoproterozoic. ...A paucity of robust geochronological and isotope geochemical data and the perpetuation of poor-quality data have hampered petrogenetic interpretations, and regional and global tectonic correlations. Here, we report new zircon U–Pb and Hf isotopic data, and new muscovite 40Ar/39Ar data from key stratigraphic intervals in the Archean nucleus and the North Singhbhum Mobile Belt. Together with critical scrutiny of available geochronological data, it is clear that the Older Metamorphic Tonalite Gneiss (with several Hadean zircon xenocrysts), the Older Metamorphic Group and parts of the Iron Ore Group were contemporaneous at ca. 3510–3375 Ma. Zircon Hf and whole-rock Nd data from these units reveal juvenile but also subchrondritic values that suggest crustal recycling operated in the Hadean and early Archean. Continued juvenile magmatic addition and crustal reworking of older portions of the craton led to the progressive emplacement of the Singhbhum Granite at ca. 3365–3285 Ma. Minor Meso- to Neoarchean granitoid emplacement, mafic dyke swarms and sedimentation completed the building of the Archean nucleus. In the early Proterozoic, supracrustal deposition and magmatism of the poorly temporally-constrained Dhanjori and Chaibasa Formations occurred along the northern margin of the craton, and equivalent units along the southern margin in the Rengali Province. In the North Singhbhum Mobile Belt, a major hiatus then occurred. Deposition and emplacement of the conformable Dhalbhum, Dalma and Chandil Formation followed, with zircon U–Pb data of 1629 ± 4 Ma from rhyolite flows in the lower Chandil Formation providing a maximum age for the underlying formations. Detrital zircon from three samples in the Dhalbhum and Chandil Formations reveal equivalent zircon populations, where >65% are juvenile to moderately evolved ca. 2550–2430 Ma grains, with additional 2800–2600 Ma, 2150–1950 Ma and ca. 1750 Ma subpopulations. Provenance for these samples is probably predominantly from the Dharwar ± Bastar Cratons to the southwest. In a tectonic context, arc-related orogenesis at ca. 1.6 Ga started from the southern tip of India and propagated northwards to the Singhbhum Craton to explain derivation of detritus from the topographically-higher Dharwar ± Bastar Cratons. Slab roll-back induced separation in the Mesoproterozoic before final re-amalgamation at ca. 1.0 Ga is evidenced by widespread Grenvillian-aged magmatism, metamorphism and deformation in Peninsular India, including syenitic rocks in the Chandil Formation, zircon Pb-loss recorded in other samples and a muscovite 40Ar/39Ar age along the Singhbhum Shear Zone of 970 ± 8 Ma. No further tectonothermal or magmatic activity is known in the Singhbhum Craton or supracrustal provinces, attesting to its final stabilization in the earliest Neoproterozoic.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The De’erni Cu–Zn-Co deposit is a typical altered ultramafic-hosted volcanogenic massive sulfide deposit comprising four lenticular main orebodies (0.57 Mt Cu, 1.27% Cu average ore grade; 0.03 Mt Co, ...0.09% Co average ore grade; 0.16 Mt Zn, 1.04% Zn average ore grade) hosted in serpentinite and a 200-m-thick basalt was found below the No. I orebody. Serpentinite spinel Al
2
O
3
, TiO
2
, Cr#, and Mg# indicate a mantle-source. Serpentinite magmatic-hydrothermal genesis is indicated by the following: (i) high Rb/Y and Th/Zr ratios, low Nb/Zr ratios, and low δ
65
Cu values; (ii) altered magnetite rims on spinel being characterized by high Cr, Ni, and Ti, and low Ga contents; (iii) pyrite appears along the boundary of spinel grains and has a higher Co and Ni content than pyrite in ores. Therefore, the ultramafic host rocks are formed by strong fluid alteration of primary mantle rocks. The compositional zoning of Co, Cu, and Zn in euhedral coarse-grained pyrite from massive sulfide ore suggests that metal enrichment was associated with three fluid phases, with a clear temporal interval between the fluid activity that introduced Co/Cu enrichment and Zn enrichment (Zn-rich veins in magnetite cross-cut early spinel). Serpentinite exhibits a higher Zn content and decoupling of Ni and Co contents compared to Dur’ngoi ophiolite serpentinite distal from the orebody, implying primary ultramafic rocks may have provided Co to the ores. The apparently high Cu content of the Dur’ngoi ophiolite basalt in comparison with ophiolite basalts worldwide indicates basalt may have supplied the Cu.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Titanite can be found in rocks of wide compositional range, is reactive, growing or regrowing during metamorphic and hydrothermal events, and is generally amenable to U–Pb geochronology. Experimental ...evidence suggest that titanite has a closure temperature for Pb ranging from 550 to 650°C, and thus titanite dates are commonly interpreted as cooling ages. However, this view has been challenged in recent years by evidence from natural titanite which suggests the closure temperature may be significantly higher (up to 800°C). Here, we investigate titanite in an enclave of migmatitic gneiss included within a granite intrusion. The titanite crystals exhibit textural features characteristic of fluid‐mediated mass transfer processes on length scales of <100 µm. These textural features are associated with variation in both Pb concentrations and distinct U–Pb isotopic compositions. Zr‐in‐titanite thermometry indicates that modification of the titanite occurred at temperatures in excess of 840°C, in the presence of a high‐T silicate melt. The Pb concentration gradients preserved in these titanite crystals are used to determine the diffusivity of Pb in titanite under high‐T conditions. We estimate diffusivities ranging from 2 × 10−22 to 5 × 10−25 m2/s. These results are significantly lower than experimental data predict yet are consistent with other empirical data on natural titanites, suggesting that Pb diffusivity is similar to that of Sr. Thus our data challenge the wide‐held assumption that U–Pb titanite dates only reflect cooling ages.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Placing spatial and temporal constraints on deformation, uplift and exhumation using thermochronology methods can shed light on Cenozoic orogenic evolution in the Kuqa foreland. New apatite (U–Th)/He ...and previously published apatite fission track thermochronology are combined with vitrinite reflectance data and modeling to compile a low temperature, multi-stage thermal history of tectonic uplift/thrust and exhumation. A rapid uplift and exhumation event originated in South Tianshan during the Eocene (~46Ma), with systematic younging of mean apatite (U–Th)/He ages from north to south (from the margin towards the interior). Uplift and exhumation south edge of the Biyoulebaoguzi anticline in the northern monocline belt at ~36Ma with more than 3400m of stratum denuded. Subsequently, deformation and uplift south edge of the Biyoulebaoguzi anticline in the northern monocline belt at ~36Ma with more than 3400m of stratum denuded. Subsequently, deformation and uplift extended to the northern edge of Kelasu–Yiqikelike at ~10Ma and then at ~6Ma, the Kanyaken anticline formed and uplifted resulting in 3000–3700m of overburden erosion. The data support sequential southward propagating deformation and uplift (inferred exhumation) in the north Kuqa Depression during the Cenozoic, probably as a result of the collision of India with Asia far to the south of the Tianshan.
Display omitted
•We compiled thermal history and quantified Cenozoic uplift/exhumation history.•A rapid uplift and exhumation originated in South Tianshan during the Eocene.•Initial timing of exhumation systematically became younger from the north to south.•Eroded thickness gradually decreases from the basin margin to the interior.•Folding and thrusting propagated sequentially southward during the Cenozoic.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
ABSTRACT
Mantle-derived mafic magmas may be the source of ore-forming metals in large Cu porphyry systems, but evidence of primary petrogenetic and metallogenetic processes can be masked by ...hydrothermal alteration. The Baguio district of Northern Luzon, Philippines is a world-class mineral province containing approximately 40 Moz of gold and 5 Mt of copper, distributed across many porphyry Cu and epithermal Au deposit systems which are spatially related to Pliocene pre-ore Liw-Liw Creek (LCC) basaltic dikes (3·59–4·73 Ma) and a syn-ore plagioclase–hornblende diorite porphyry (2·81–2·98 Ma). A range of phenocryst phases (plagioclase, amphibole and clinopyroxene) are well preserved in both the basaltic dike suite and diorite porphyry suite, and provide an excellent natural laboratory to investigate magmatic processes and the relationship between metallogenesis and mafic magma. Widespread normally zoned clinopyroxene and amphibole grains in the basaltic dike suite show sharp decreases in Mg#, but increasing Mn, Sr, Cu, Y, Zr and REE from core to rim. Mixing of evolved felsic magma into the mafic magma is the most likely cause of these trends as fractional crystallization would typically result in gradual variations. In the diorite porphyry suite, reversely zoned amphibole is characterised by sharp increases in Mg#, Cu and Ni, but decreasing Mn, while oscillatory zoned plagioclase with distinct regions of patchy zonation shows repeated variations of An, Mg, Fe and Sr from core to rim. These signatures indicate the addition of basaltic magma to the diorite porphyry magma. The modeled Mg# of the melts (estimated assuming mineral-melt equilibrium) is also consistent with magma mixing. For example, the high Mg# of 66–72 and low Mg# of 38–44 estimated from the LLC clinopyroxene cores and rims, respectively, support the presence of basaltic magma, mixed with evolved felsic magma. All normally zoned clinopyroxene and amphibole in the basaltic dike suite and reversely zoned amphibole in the diorite porphyry suite show consistent increases in Cu from core to rim, suggesting relative enrichment of Cu in both types of injected magma. The pre-ore basaltic and ore-forming dioritic hybrid melts are estimated to have contained 45–96 ppm and 319–351 ppm Cu, respectively, based on Cu partition coefficients and zone area percentage. The Cu content of the basaltic hybrid melt is typical of arc magmas (Cu 50–100 ppm), whereas the Cu in the dioritic melt was 3–6 times higher than typical arcs magma. Both the clinopyroxene-melt thermobarometer and Al-in-hornblende geobarometer indicate similar crystallization pressures for both suites (8·6∼8·8, 4·4∼4·7, 2·1∼2·8 kbar), suggesting that both pre-ore basaltic and syn-ore dioritic suites formed in different magma chambers at similar depths. The addition of Cu enriched mafic magma may contribute ore-forming elements to the mineralising magmas and significantly increase the mineralization potential of coeval felsic rocks. Studies of phenocrysts have the potential to elucidate the role of magmatic process in the formation of porphyry systems and allow for the recognization of the key characteristics of fertile magmatic systems.
Titanite is a common accessory mineral that is useful in determining both age (U-Pb isotopes) and pressure-temperature (P–T) conditions (trace-element composition: Zr, rare earth elements (REE)). ...However, titanite has a propensity to recrystallize during metamorphism, fluid flow, and deformation, which can result in modifications to its isotopic and trace-element compositions. This modification has implications for the interpretation of titanite dates and the evaluation of pressure–temperature–time paths. The impact of deformation and recrystallization on trace-element mobility in titanite is investigated through microstructural and compositional mapping of titanite crystals from a sheared orthogneiss within an ultrahigh-pressure domain of the Western Gneiss Region (WGR), Norway. Results show that optically coherent titanite single crystals deformed in the dislocation creep regime and recrystallized by the process of grain-boundary migration, forming aggregates of titanite grains. Some of the aggregate grains record Caledonian-exhumation dates, whereas others have an inherited isotopic composition. Individual grains within the aggregate, regardless of their U-Pb isotopic composition, contain patchy zoning that formed during syn- to post-recrystallization fluid alteration and that is characterized by generally decreasing Ca and Ti and increasing Al and Fe from cores to rims. However, Zr and Sr concentrations are broadly zoned with respect to the long axis of the host crystal, without regard for the aggregate grain boundaries. REE do not show any obvious correlation with microstructure or age. These results indicate that many trace elements in titanite are unaffected by multi-stage, deformation-driven recrystallization; in contrast, Pb is variably mobile in these deformed titanite crystals. The combination of microstructural and high-spatial resolution geochemical and isotopic data reveals the potential extent of decoupling between the U-Pb isotopic system and the behavior of trace elements as pressure–temperature conditions change through time.
•Single titanite crystals within a shear zone consist of an aggregate of dynamically recrystallized grains.•The titanite grains underwent a combination of dislocation creep and recrystallization via grain-boundary migration.•U-Pb isotopes were variably affected by deformation and recrystallization, whereas most trace elements were unaffected.•U-Pb isotopes may be decoupled from trace elements in titanite.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
