Porphyritic Quartz Monzonite Research Articles

Petrogenesis of the Eocene Yulong potassic intrusion in non‐subduction setting in the Sanjiang Tethys

The giant Yulong porphyry Cu (‐Mo‐Au) deposit was formed in a post‐collisional setting in eastern Tibet, which is associated with Eocene potassic to ultrapotassic felsic intrusive rocks. The origin of the Yulong potassic intrusion remains highly disputed. Hence, we present new zircon U–Pb ages, whole‐rock geochemistry and zircon Lu‐Hf isotopes for the Yulong intrusion. Zircon U–Pb dating from the porphyritic monzogranite and porphyritic quartz monzonite yield ages of 41.1 ± 0.2, 40.8 ± 0.1 and 40.5 ± 0.2 Ma, respectively. Samples from the Yulong intrusion exhibit high K2O (4.13–4.85%), and high K2O/Na2O (1.00–1.25), [La/Yb]n (30.37–40.37) and Sr/Y (57.86–87.68) ratios, low Mg#, MgO, Ni, and Cr contents, enrichment in light rare earth elements (LREEs) and depletion of high‐field‐strength elements (HFSEs, e.g., Nb, Ta, and Ti). Zircon grains from this study have mostly positive εHf(t) values (+1.6 to +2.9), and crustal model ages (TDMC) of 0.90–1.19 Ga. These features suggest that the Yulong intrusion is derived from a thickened juvenile lower crust. During the Permian to late Triassic, Jinshajiang‐Ailaoshan Palaeo‐Tethyan oceanic subduction from the eastern margin of the North Qiangtang produced metasomatic domains within the continental lithospheric mantle and lower crust. During the late Eocene, the continuing India‐Asia continental collision may have preferentially overthickened the crust. Convective removals in the lower part of the thickened lithosphere resulted in the hot asthenosphere upwelling along the Jinshajiang‐Ailaoshan Suture, which induced the partial melting of the residual metasomatized lithospheric mantle, as well as the thickened lower crust in the Eocene, which formed the Yulong intrusion.

Connected volcanic and plutonic association by crystal-melt segregation in the Daiyunshan volcanic field, SE China

The Daiyunshan volcanic field is one of the largest volcanic fields in the volcanic-plutonic complex belt along the coast of SE China, which records a long volcanic activity history from the Late Jurassic to the Late Cretaceous. In this paper, we conduct comprehensive petrological, geochemical, isotopic and zircon trace element analyses for two representative calderas (Shiniushan and Yunshan) to reveal the crystal-melt segregation and magma recharge processes of the Daiyunshan volcanic field. Systematic LA-ICP-MS zircon U-Pb dating and isotope analyses reveal that the porphyritic quartz monzonite, porphyritic granite and rhyolite of the Shiniushan caldera have identical crystallization ages (97–94 Ma) and consistent Nd-Hf isotope compositions [εNd(t) = −3.6 to −2.8; zircon εHf(t) = −2.7 to 1.8], which are consistent with those of the porphyritic quartz monzonite and rhyolites in the nearby Yunshan caldera, indicating that the magmas of the two calderas were derived from a common magma source region. Volcanic-plutonic rocks from two calderas display metaluminous to peraluminous features and have low MgO, FeOT, Ni and Cr contents. We thus suggest that their parental magmas were derived by remelting of pre-existing crust with contributions of juvenile components. The Shiniushan porphyritic granite and rhyolite and the Yunshan rhyolites are characterized by distinctly negative Eu anomalies and depletions of Ba, Sr, P and Ti, while the porphyritic quartz monzonites from both calderas show complementary geochemical signatures, such as positive Ba anomalies and neglectable Eu anomalies. The back-scattered electron (BSE) images and energy-dispersive X-ray spectrometry (EDS) phase mapping of the Shiniushan porphyritic quartz monzonite reveal textural indicators of crystal accumulation, such as imbrication and synneusis of plagioclase phenocrysts. Their interstitial assemblages of K-feldspar, quartz and plagioclase commonly resemble the phenocryst assemblages of porphyritic granite. We believe that the Shiniushan porphyritic granite and rhyolite and Yunshan rhyolites represent extracted melts from the mush reservoir, while porphyritic quartz monzonites in both calderas are inherent cumulates that have lost interstitial melts. Therefore, our study shows that the Late Cretaceous volcanic-plutonic rocks in the Daiyunshan volcanic field should be connected by crystal-melt segregation processes. Furthermore, a typical zigzag variation in zircon εHf(t) values is shown by the Late Jurassic to Late Cretaceous volcanic-plutonic rocks from the Daiyunshan volcanic field, indicating variable contributions of asthenospheric mantle-derived melts and the multistage slab rollback of the subducting paleo-Pacific plate beneath SE China.

A Comparative Study of Porphyry-Type Copper Deposit Mineralogies by Portable X-ray Fluorescence and Optical Petrography

Porphyry-type deposits are crucial reserves of Cu and Mo. They are associated with large haloes of hydrothermal alteration that host particular mineral assemblages. Portable X-ray fluorescence analysis (pXRF) is an increasingly common tool used by mineral prospectors to make judgments in the field during mapping or core logging. A total of 31 samples from 13 porphyry copper deposits of the Western Cordillera were examined. Whole-rock composition was estimated over three points of analysis by pXRF. This approach attempts to capture the rapid and sometimes haphazard application of pXRF in mineral exploration. Modes determined by optical petrography were converted into bulk rock compositions and compared with those determined by pXRF. The elements S, Si, Ca, and K all were underestimated by optical mineralogy, and the elements Cu, Mo, Al, Fe, Mg, and Ti were overestimated by optical mineralogy when compared with pXRF results. Most of these porphyry samples occur in veined porphyritic quartz monzonite that is characteristic of these deposits. Sulfide and silicate vein stockworks are pervasive in most of the samples as well as dissemination of sulfides outwards from veinlets. Ore minerals present include chalcopyrite and molybdenite with lesser bornite. Chalcocite, digenite, and covellite are secondary. Potential sources of analytical bias are discussed.

Tracking crystal-melt segregation and magma recharge using zircon trace element data

The Cretaceous Yunshan caldera complex in SE China consists of an unusual coexisting assemblage of peraluminous and peralkaline rhyolites and a resurgent intra-caldera porphyritic quartz monzonite. In this study, we use zircon trace element data to study the compositional differences of zircons from cogenetic magmas and to track the evolution of the entire magmatic system. Our results indicate that the zircons from the peraluminous and peralkaline rhyolites formed from highly evolved compositions with high Hf concentrations and low Ti contents, and low Th/U and Zr/Hf ratios, which are distinct from those of the intrusive porphyritic quartz monzonite. Zircons from the peraluminous and peralkaline rhyolites display overlapping Zr/Hf and Hf, but the zircons from the peralkaline rhyolites have extremely low Eu/Eu* ratios (<0.1) and Ti contents (2.26–13.3 ppm). The lack of overlapping zircon trace element compositions between the volcanic and intrusive caldera units is interpreted to represent crystal–melt segregation processes. In addition, zircon grains from the porphyritic quartz monzonite and a few zircon grains from the peraluminous rhyolite display distinctly bright rims and whole grains in cathodoluminescence imaging, which have high Ti, Zr/Hf, and Eu/Eu*, and are similar to those of zircons from the mafic microgranular enclave within the porphyritic quartz monzonite. We interpret these signatures to reflect crystallization from a relatively hot and less evolved magma indicating a magma chamber recharge event. We further developed a model in which the magmas of the peraluminous and peralkaline rhyolites were successively extracted from a primitive crystal mush by crystal–melt segregation with a rejuvenation of the crystal mush after the extraction of the peraluminous rhyolitic melt, leaving behind residual mushes solidified as porphyritic quartz monzonite. Our study shows that trace element analyses of zircons can effectively be used to pinpoint multiple crystal–melt segregation and melt extraction events as well as magma recharge processes in silicic magmatic systems.

Bavsiite, Ba2V2O2[Si4O12], mineral data and crystal structure

AbstractBavsiite from the type locality Gun Claim, Yukon Territory, Canada, occurs as millimetre-sized sky-blue platy crystals in a barium-rich low-temperature skarn related to a porphyritic quartz monzonite stock. Associated minerals are alstonite, baryte, celsian, diopside, fresnoite, mica, suzukiite, walstromite, witherite and minerals of the cerchiaraite group. Bavsiite is optical uniaxial (+), with ω = 1.725(3) and ε = 1.750(3) (589 nm) and pleochroic. Electron microprobe analyses yielded the empirical formula Na0.02Ba1.98Ti0.16Fe2+0.03V4+1.80 Al0.05Si4.00O14 based on 14 oxygen atoms, the simplified chemical formula is Ba2V2Si4O14. Bavsiite is tetragonal, space group I4/m, a = 7.043(1), c = 11.444(2) Å and Z = 2 obtained from single crystal data at 100 K, which are in good agreement with cell parameters from powder diffraction data at 293 K: a = 7.051(1) Å and c = 11.470(1) Å. The eight strongest lines of the powder X-ray diffraction pattern are [d, Å (I,%)(hkl)]: 3.76(30)(112), 3.36(44)(013), 3.004(100)(022), 2.493(43)(220), 2.486(67)(114), 2.286(24)(222), 1.785(39)(116) and 1.763(25)(040). The crystal structure was refined to R = 0.0159 based upon 312 unique reflections with I &gt; 2σ(I). The crystal structure of bavsiite comprises unbranched single [Si4O12]8– rings connected by [VO5]6– square pyramids and BaO12 polyhedra. It can also be considered as cage–like [Si4V2O18]12– clusters built by four SiO4 tetrahedra and two VO5 square pyramids. These clusters are cross–linked to form a pseudo-two-dimensional network (2D) parallel to (001) containing empty channels along the a axis and the 2D networks held together by Ba2+ ions located in channels parallel to the c axis. The structural formula is Ba2V2O2[Si4O12]. Bavsiite is polymorphic to suzukiite, BaVSi2O7, which is orthorhombic.

Phyllic alteration and the implications of fluid composition at the Copper Flat hydrothermal System, New Mexico, USA

The Copper Flat hydrothermal system in Hillsboro, New Mexico, USA, is hosted by a partially brecciated porphyritic quartz monzonite intrusive body. Igneous rocks are alkaline to calc-alkaline, and chondrite-normalized rare earth element (REE) plots show enrichment in REEs that is consistent with other regional Laramide igneous rocks. Five assemblages of weak to moderate intensity phyllic alteration with distinct paragenetic relationships exist at the deposit and are classified as: early phyllic, quartz-sericite-pyrite (QSP), sericite-quartz, sericite-carbonate and late QSP. Carbonate is common and is part of some phyllic and the potassic alteration assemblages. Carbonates and phyllosilicates were analyzed by electron microprobe. White micas show substantial substitution of Al by Fe and Mg, and secondary biotite is Mg-rich. Relative to other porphyry Cu systems, the micas from Copper Flat contain, on average, greater F. Carbonates from veins and the replacement of mafic silicates and feldspars were determined to be mostly calcite, but reduced metal carbonates such as ankerite and rhodochrosite are also present in the alteration assemblages. The fluid(s) responsible for alteration are inferred to be CO2-rich and pH neutral as interpreted from the widespread presence of carbonates in both the potassic and phyllic alteration zones, and the white mica composition. Carbonate mineral compositions and absence of sulfates in the potassic alteration suggest that the hydrothermal fluids were not highly oxidized and were sulfur-poor. These features of alteration and geochemistry at Copper Flat are atypical of most porphyry Cu-Mo deposits in the southwestern U.S. and may be more characteristic of porphyry Cu-Au and porphyry Mo deposits.

Highly differentiated magmas linked with polymetallic mineralization: A case study from the Cuihongshan granitic intrusions, Lesser Xing'an Range, NE China

The genetic link between granitoids and polymetallic skarn mineralization has remained equivocal. The Cuihongshan skarn-porphyry W-Mo-Pb-Zn-(Fe-Cu) deposit in the eastern part of the Central Asian Orogenic Belt provides a unique example to address this issue. The major rock types in the mine area are Early Paleozoic intrusions composed of biotite syenogranite and biotite porphyritic granite and Early Mesozoic intrusions represented by porphyritic quartz monzonite, biotite monzogranite, and porphyritic granite. The diagnostic mineralogical and geochemical features indicate that the rocks belong to A2-type granites. The Early Paleozoic suite shows zircon U-Pb ages of ~501Ma, and εHf(t) values of −4.4 to +2.7 and +2.4 to +7.6, respectively. In combination with their coherent geochemical trends, these rocks are inferred to be products of in-situ differentiation. Although the Mesozoic suite shows crystallization ages of 194–196Ma, εHf(t) values are in the range of −2.5 to +7.5 for the porphyritic quartz monzonite, the −1.8 to +4.5 values for the monzogranite and the +2.3 to +8.0 range for the porphyritic granite. The porphyritic quartz monzonite displays distinct mineral assemblage and shows significant compositional gap with the other two lithofacies. In contrast, the monzogranite and porphyritic granite have similar geochemical features, and are thus inferred to be co-magmatic. Considering the high SiO2 contents, variable εHf(t) (−4.4 to +8.0) and εNd(t) values (−8.4 to +0.28) for the two suites, we infer that both episodes of granitoid magmatism resulted from partial melting of crustal materials with a mixed source containing varying proportions of juvenile and Precambrian crustal components. The Early Mesozoic porphyritic granite shows a highly evolved F-rich geochemical affinity, and experienced magma-fluid interaction. Cassiterite from the calcic skarn and the magnesian skarn that coexists with magnetite orebodies shows a mean U-Pb age of 195.4±1.9Ma and 191.2±7.5Ma respectively, indicating that the mineralization is genetically related to the Mesozoic granitic rocks. We infer that halogen-rich magmatic-hydrothermal fluids were derived from the Early Mesozoic highly fractionated magma, and the spatial association of the metallic elements with different geochemical behavior in the Cuihongshan deposit is correlated to multiple stages of evolution of halogen-rich magmatic-hydrothermal fluids.

Zircon U–Pb geochronology and geochemistry of the Cerro Colorado porphyry copper deposit, northern Chile

Porphyry Copper Deposits (PCDs) dominantly form in convergent plate margins genetically related to volcanic arcs. However, their temporal relationships with active volcanism are less clear. Active volcanic activity is often considered to impede the formation of PCDs and some workers have concluded that PCD formation must take place at times of volcanic quiescence or at a waning stage of volcanism. However, several studies have documented evidence suggesting syn-eruption PCD formation. A combination of radiometric dating, geochemistry studies and observations of rock cores from the Cerro Colorado PCD, a BHP Billiton property located in N. Chile, provides evidence compatible with syn-volcanic PCD formation within a volcanic edifice.Textural observations at both hand specimen and microscopic scales combined with new LA-ICPMS and SHRIMP dating of zircons suggest the intrusive history of the Cerro Colorado area can be separated into two main units: a porphyritic tonalite ca. 53.5 Ma and a porphyritic quartz monzonite ca. 50 Ma. There is also evidence for crystallisation at ca. 60 Ma, but a corresponding distinct lithology was not identified. A quartz porphyry unit previously identified as the youngest intrusive body is reinterpreted as an altered equivalent of the monzonite. The youngest intrusive units are represented by porphyritic granodiorite with an age 51–50 Ma. These units only show minor metal mineralisation suggesting that the main phase of mineralisation in the Cerro Colorado mine occurred over a few million years, bracketed by the two main pulses of igneous intrusion, which are consistent with documented Ar–Ar ages. Re–Os ages reported by previous studies suggest an earlier phase of mineralisation at ca. 56–54 Ma. U–Pb dating of zircon from a volcanic-related breccia that cuts the host rocks of the Cerro Colorado Mine reveals a phase of volcanic activity at ca. 57 Ma, after formation of the regional Cretaceous Cerro Empexa Formation. This age range overlaps the ages derived for the intrusive porphyry units suggesting a close temporal relationship between volcanism and the ore-forming subvolcanic intrusions in Cerro Colorado. A link between active volcanism and mineralisation is reinforced by the ultrafine-grained matrix and the presence of strong brecciation associated with the monzonite-quartz porphyry stock suggesting decompression and volatile release have taken place during emplacement.

Geochemical constraints on the link between volcanism and plutonism at the Yunshan caldera complex, SE China

The Yunshan caldera complex is part of a larger scale, ca. 2000-km-long volcanic–plutonic complex belt in the coastal region of SE China. The volcanic rocks in the caldera complex are characterized by high-silica peraluminous and peralkaline rhyolites associated with an intracaldera porphyritic quartz monzonite pluton. In this study, we present zircon U–Pb, Hf and stable O isotopes along with geochemical data of both volcanic and plutonic rocks to evaluate the potential petrogenetic link between volcanism and plutonism in the Yunshan caldera complex. SHRIMP zircon U–Pb geochronology of both volcanic and plutonic rocks yields almost identical ages ranging from 95.6 to 93.1 Ma. The peraluminous and peralkaline rhyolites show negative anomalies of Sr, P, Ti and Ba and to a lesser extent negative Nb and Ta anomalies, along with positive Rb anomalies and ‘seagull-like’ rare earth element (REE) patterns with negative Eu anomalies and low (La/Yb)N ratios. The intracaldera porphyritic quartz monzonite displays minor negative Rb, Nb, Ta, Sr, P and Ti anomalies and a positive Ba anomaly with REE patterns characterized by relatively high (La/Yb)N ratios and lack significant Eu anomalies. The peraluminous and peralkaline rhyolites and the porphyritic quartz monzonite exhibit consistent e Nd(t) of − 3.7 to − 2.2 and display zircon e Hf(t) values of − 2.1 to 3.7. They further have similar, mantle-like, zircon oxygen isotopic compositions (δ18OVSMOW mainly = 4.63 to 5.76‰). We interpret these observations to be in agreement with a crystal mush model in which the parental magma of the volcanic and plutonic rocks of the Yunshan caldera complex was likely produced by interaction of asthenosphere melts with subduction-influenced enriched mantle wedge. The peralkaline rhyolites are interpreted to represent the most differentiated magma that has subsequently experienced significant fluid–melt interactions, whereas the porphyritic quartz monzonite may be representative of the residual crystal mush. The Yunshan rhyolites typically match the geochemical characteristics of ‘hot-dry-reduced’ rhyolites indicating that, during the late Cretaceous, the tectonic setting of SE China changed from a compressional environment to an extensional environment, i.e., from an arc into a back-arc setting. Our results imply that volcanic and plutonic rocks in caldera systems may provide unique constraints on the evolution of the magmatic system in which both the erupting melt and the residual crystalline material are being preserved.

Petrogenesis of the postcollisional Middle Devonian monzonitic to granitic magmatism of the Sierra de San Luis, Argentina

Middle Devonian granitoids intruded the Eastern Sierras Pampeanas basement ca. 600km east of the inferred proto-Pacific margin of Gondwana along which a ca. 390Ma collisional event developed. In the Sierra de San Luis, voluminous Middle Devonian (393–382Ma) batholiths are composed of I- to A-type hybrid Monzonite and Granite suites. Shoshonite and subordinated high-K series, stocks, synplutonic dikes and enclaves make up the Monzonite Suite; rocks are metaluminous alkali–calcic magnesian porphyritic or equigranular monzonite, quartz monzonite, monzodiorite and scarce monzogabbro. High-K and subordinated shoshonite series metaluminous to mildly peraluminous magnesian alkali–calcic to calc–alkalic porphyritic or equigranular quartz monzonite, granodiorite, monzogranite and equigranular leucomonzogranites make up the Granite Suite plutons and batholiths. Only a small group of highly evolved granites are ferroan. SiO2 (46–62%), Cr, Ni, V, Sc, LILE, LREE, Th, Zr and variable, Sr/Y, (La/Yb)N and (Tb/Yb)N, smooth Eu/Eu*, moderate Na2O (ca 3.5), and troughs at Nb and Ta for Monzonite Suite rocks suggest an subduction-related enriched lithospheric mantle source. Sm–Nd data (TDM 0.98–1.08Ga, εNd(380Ma) 0.66–1.47) and 87Sr/86Sri (0.703520–0.704203) are compatible with an enriched mantle source. The metaluminous porphyritic quartz monzonite–monzogranite and the mildly peraluminous equigranular biotite monzogranites of the Granite Suite are characterized by relatively moderate Al2O3, CaO, and 87Sr/86Sri, high LILE, Cr, variable Sr/Y, (La/Yb)N and Eu/Eu* and low Rb/Sr (<1.2) suggest a mafic source. The porphyritic monzogranite (TDM 1.20–1.28Ga, εNd(380Ma) −3.02 to −3.3, 87Sr/86Sri 0.706578–0.707027) and the biotite monzogranites (TDM 1.31Ga, εNd(380Ma) −3.3, 87Sr/86Sri 0.707782) would share a common source. The equigranular alkali–calcic leucomonzogranites are characterized by Rb/Sr >1.5, ASI 1.05–1.18, and Ga/Al 2.6–3.9, εNd(380Ma) −3.74 to −3.95 and (87Sr/86Sr)i 0.710743–0.712955 which would point to metasedimentary or felsic igneous crustal sources. Nevertheless their TDM 1.36–1.38Ga is considerably younger than the mean 1.8–1.6Ga Eastern Sierras Pampeanas crustal residence age and less radiogenic. Middle Devonian magmatism would record an episode of crustal growth by enriched mantle derived magma input and variable degrees of partial melting of a lower crustal source at the waning stages of the Achalian orogeny.

Geological, geochronological, and mineralogical constraints on the genesis of the Chengchao skarn Fe deposit, Edong ore district, Middle–Lower Yangtze River Valley metallogenic belt, eastern China

The Edong ore district is located within the westernmost Middle–Lower Yangtze River Valley metallogenic belt (MLYRB), and hosts the largest concentration of skarn Fe deposits in China, although the origin of these deposits remains controversial. The Chengchao deposit is the largest skarn Fe deposit so far discovered within the MLYRB, and provides a good opportunity to address the debate surrounding the origin of these skarn Fe deposits. Here, we present geological, geochronological, and mineralogical data from the Chengchao skarn deposit and associated intrusions, and discuss the relationships between granitoids and mineralization in the Chengchao deposit.The NW–SE-striking orebodies in the study area have porphyritic quartz monzonite and/or granite footwalls, and Triassic marble or diorite hangingwalls, indicating a spatial relationship between these intrusions and Fe mineralization. Zircon U–Pb data from the granite, porphyritic quartz monzonite, diorite, and porphyritic diabase dike within the deposit show ages of 129±1, 128±1, 140±1, and 126±1Ma, respectively. These ages and the previously reported ages on the timing of mineralization suggest that the porphyritic quartz monzonite and granite are coeval with the formation of the skarn Fe deposit. Our data confirm that the granitic rocks are temporally associated with Fe mineralization.The prograde substage of skarn development is characterized by two stages of andradite (Adr98-38Grs61-2Prp2-0Sps1-0Alm1-0) and diopside (Di95-61Hd37-5Jo3-0), including an early stage of garnet and pyroxene formation that is genetically associated with the mineralization. The early stage garnets are more andradite-rich (Adr98-50Grs49-2Prp1-0Sps1-0Alm0) than the late veinlet garnets characterized by intermediate grandite compositions (Adr67-37Grs61-31Prp2-0Sps1-0Alm1-0). The early stage pyroxenes (Di95-74Hd26-5Jo1-0) are compositionally distinct from the late stage pyroxenes (Di84-61Hd37-16Jo3-0). Compositional variations of early stage garnets in the zoned skarns indicate that skarn formation and Fe mineralization are genetically associated with the porphyritic quartz monzonite and granite intrusions. The geological, geochronological, and mineralogical evidence indicates that the porphyritic quartz monzonite and granite intrusions in the Chengchao Fe deposit are spatially, temporally, and genetically associated with Fe mineralization.

Geochronology and geochemistry of Cretaceous Nanshanping alkaline rocks from the Zijinshan district in Fujian Province, South China: Implications for crust–mantle interaction and lithospheric extension

In situ zircon U–Pb ages and Hf isotopic data, major and trace elements, and Sr–Nd–Pb isotopic compositions are reported for Nanshanping alkaline rocks from the Zijingshan district in southwestern Fujian Province (the Interior or Western Cathaysia Block) of South China. The Nanshanping alkaline rocks, which consist of porphyritic quartz monzonite, porphyritic syenite, and syenite, revealed a Late Cretaceous age of 100–93Ma. All of the rocks show high SiO2, K2O+Na2O, and LREE but low CaO, Fe2O3T, MgO, and HFSE (Nb, Ta, P, and Ti) concentrations. These rocks also exhibit uniform initial 87Sr/86Sr ratios of 0.7078 to 0.7087 and εNd(t) values of −4.1 to −7.2, thus falling within the compositional field of Cretaceous basalts and mafic dikes occurring in the Cathaysia Block. Additionally, these rocks display initial Pb isotopic compositions with a 206Pb/204Pbi ratio of 18.25 to 18.45, a 207Pb/204Pbi ratio of 15.63 to 15.67, and a 208Pb/204Pbi ratio of 38.45 to 38.88. Combined with the zircon Hf isotopic compositions (εHf(t)=−11.7 to −3.2), which are different from those of the basement rocks, we suggest that Nanshanping alkaline rocks were primarily derived from a subduction-related enriched mantle source. High Rb/Sr (0.29–0.65) and Zr/Hf (37.5–49.2) but relatively low Ba/Rb (4.4–8.1) ratios suggest that the parental magmas of these rocks were most likely formed via partial melting of a phlogopite-bearing mantle source with carbonate metasomatism. The relatively high SiO2 (62.35–70.79wt.%) and low Nb/Ta (10.0–15.3) ratios, positive correlation between SiO2 and (87Sr/86Sr)I, and negative correlation between SiO2 and εNd(t) of these rocks suggest that the crustal materials were also involved in formation of the Nanshanping alkaline rocks. Combined with geochemical and isotopic features, we infer magmatic processes similar to AFC (assimilation and fractional crystallization) involving early fractionation of clinopyroxene and olivine and subsequent fractionation of biotite-dominated assemblages coupled with a lesser amount of crustal contamination, thereby forming the Nanshanping alkaline rocks. The Nanshanping alkaline rocks appear to be associated with an extensional environment in the Cathaysia Block. This extensional regime could have resulted in the slab break-off and rollback of the subducting paleo-Pacific plate and the upwelling of the asthenospheric mantle, which induced partial melting of the enriched lithospheric mantle in the Cretaceous.

Paleoproterozoic S- and A-type granites in southwestern Zhejiang: Magmatism, metamorphism and implications for the crustal evolution of the Cathaysia basement

Paleoproterozoic granites and metamorphic rocks of the Badu complex, the oldest rocks found in Cathaysia Block, provide a window for investigating the crustal evolution of the Cathaysia basement. SHRIMP and LA-ICP-MS zircon U–Pb ages of five representative granite samples from Jinluohou (Lizhuang) and Jingju granitic complexes indicate that the magmatism took place during Paleoproterozoic, and overprinted by early Mesozoic thermal event. The Jinluohou garnet-bearing biotite granite (1878±28Ma) has high A/CNK (1.28–1.42), low contents of P2O5 and low FeOT/(FeOT+MgO). It contains a large amount of biotites and garnets with minor inherited zircons but no primary muscovites, showing the S-type granite affinity. It was formed at low water fugacity and high Zr saturation temperature (792–809°C). The Jingju medium-coarse grained K-feldspar granite (1861±35Ma), Jingju medium-fine grained K-feldspar granite (1849±30Ma) and Jinluohou gneissic granodiorite (1877±10Ma) can reach strongly peraluminous (A/CNK=0.97–1.26), are enriched in alkalis and HFSE (Zr, Nb, Ce, Y) and have high Ga/Al and FeOT/(FeOT+MgO) ratios. Their high Zr saturation temperatures (840–854°C, most of them are higher than 830°C) together with high Rb/Nb and Y/Nb ratios suggest that they belong to the A2 subgroup of A-type granites. The ages of inherited zircon cores from Jinluohou garnet-bearing biotite granite (2088–2929Ma) reveal the existence of the Archean basement, and the Hf and Nd isotopes and chemical compositions suggest that these S- and A-type granites were originated from the Paleoproterozoic and Archean crustal sources with different proportions of input from juvenile crust materials. The Paleoproterozoic S- and A-type granites intruded simultaneously, and formed under intraplate extensional geodynamic setting, which is an important event of episodic crustal growth and reworking. The age of Jingju porphyritic quartz monzonite (226.2±1.4Ma) and the lower intercept age of Jinluohou gneissic granodiorite, Jingju K-feldspar granite (224–231Ma) may indicate another important thermal overprinting event in this region.

Early Jurassic high-K calc-alkaline and shoshonitic rocks from the Tongshi intrusive complex, eastern North China Craton: Implication for crust–mantle interaction and post-collisional magmatism

The Tongshi intrusive complex, located within the western Shandong Province (Luxi Block) in the eastern North China Craton, comprises high-K calc-alkaline series (fine-grained quartz monzonite and porphyritic quartz monzonite) and shoshonitic series (coarse- to fine-grained porphyritic syenites). Here we report comprehensive data on petrology, geochemistry, Sr–Nd–Pb isotopes and zircon U–Pb and Hf isotopic compositions from the intrusive complex. LA–ICPMS zircon U–Pb ages show that this complex was emplaced at 180.1–184.7Ma. The fine-grained quartz monzonite and porphyritic quartz monzonite have similar major and trace elements features, implying a similar petrogenetic history. Coupled with the widespread Neoarchean inherited zircons in these rocks, the high SiO2 and Na2O as well as the low MgO contents and low Pb isotopic ratios ((206Pb/204Pb)i=15.850–16.881, (207Pb/204Pb)i=14.932–15.261, (208Pb/204Pb)i=35.564–36.562) of the quartz monzonites suggest an origin from ancient tonalite–trondhjemite–granodiorite (TTG) crust. However, their higher Nd and Hf isotopic ratios (εNd (t)=−11.7 to −7.0, εHf (t)=−25.0 to −10.3) as compared to the basement rocks indicate input of enriched lithospheric mantle-derived materials. The coarse- to fine-grained porphyritic syenites were derived from similar sources as inferred from their comparable major and trace elements contents as well as the Nd, Hf and Pb isotopic compositions. The Neoarchean inherited zircons and depletion of Nb, Ta, P and Ti in these rocks indicate the involvement of ancient crust. However, the high Nd and Hf isotopic ratios (εNd (t)=−0.8 to 1.5, εHf (t)=−4.4 to 4.8) coupled with high Pb isotopic compositions ((206Pb/204Pb)i=18.082–19.560, (207Pb/204Pb)i=15.510–15.730, (208Pb/204Pb)i=37.748–39.498) suggest that the porphyritic syenites were mainly derived from an asthenospheric mantle. Based on the geochemical and isotopic features, a magmatic process similar to MASH (melting, assimilation, storage and homogenization) is proposed for the fine-grained quartz monzonite and AFC (assimilation and fractional crystallization) is envisaged for the porphyritic quartz monzonite and porphyritic syenites. Our data suggest the interaction of various crustal and mantle sources including lower to upper crust, lithospheric mantle and asthenospheric mantle in the generation of the Tongshi intrusive complex. Sharing common characteristics with other post-collisional magmatic rocks, the high-K calc-alkaline and shoshonitic rocks from the Tongshi complex are considered to have originated in post-collisional setting, marking the beginning of lithospheric destruction in the inner domains of the NCC during Mesozoic.

Magmatic Epidote and Amphibole from the Rio Espinharas Hybrid Complex, Northeastern Brazil

The petrography and chemistry of epidote and amphibole from the Rio Espinharas hybrid complex (REHC), northeastern Brazil are reported. The Rio Espinharas complex is composed of an intimate association of diorite to shoshonitic metaluminous quartzmonzonite to slightly peraluminous syenogranite. The epidote shows four textural relationships: three are primary and one is resulting from sub-solidus reaction. Euhedral epidote is dispersed and associated mainly with biotite and amphibole. In some cases euhedral crystals of the epidote contain allanite cores, which are subhedral to anhedral and constitute in average less than 20% of the whole grain. The contact between primary epidote and plagioclase is corroded, suggesting reaction with the host-magma. Secondary anhedral epidote is rare and results from plagioclase alteration. The preservation of magmatic epidote in granitic rocks emplaced in the upper crust is attributed to rapid magma ascent, which implies fast upward transport probably by dyking associated to shear zone. The REHC occurs between two transcurrent faults that impose an elongated shape, suggesting that magma filled fractures. The time of 14 years required for dissolution zones of 0.15 mm width of epidote on porphyritic quartz monzonite, corresponds to an average ascent rate of ≥ 700 m year-1 from 7.1 to 2.9 kbar.

A Re–Os study of sulfide minerals from the Bagdad porphyry Cu–Mo deposit, northern Arizona, USA

Rhenium and osmium isotopes in sulfide minerals from the Bagdad porphyry Cu–Mo deposit have been used to determine timing of mineralization and the source of osmium and, by inference, ore metals. Molybdenite, chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units, which are characterized by moderate to strong potassic alteration (secondary biotite and K-feldspar). Rhenium concentrations in molybdenite are between 330 and 642 ppm. Four Re–Os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71.8±0.2 Ma (2σ). Analyses of a third sample from a molybdenite vein in Precambrian rocks, outside of the main ore zone, yield a weighted average age of 75.9±0.2 Ma (2σ), and provide evidence of two separate mineralization episodes. Chalcopyrite samples contain 6 to 12 ppt Os and 1.7 to 4.1 ppb Re; 187Os/188Os initial ratios are between 0.1 and 0.8. Pyrite samples have osmium and rhenium concentrations varying in the range 8–17 ppt and 3.9–6.8 ppb, respectively. Analyses from these pyrite samples yield an eight-point isochron with an age of 77±15 Ma (2σ) and an initial 187Os/188Os ratio of 2.1±0.8 (MSWD=0.90). The results presented here add to the growing body of work indicating that porphyry-type mineralization is produced by long-term, multiple episodes of magmatism and associated mineralization. The data also support the hypothesis that a significant part of the metals and magmas may have a crustal source, as has been suggested for other copper deposits and districts in Arizona.

Extension of Laramide magmatism in southwestern North America into Trans-Pecos Texas

The Red Hills intrusion hosts the easternmost porphyry copper-molybdenum system in southwestern North America and consists of quartz-sulfide stockwork veins in sericitized porphyritic quartz monzonite. Zircon U-Pb and molybdenite Re-Os analyses yield ages of 64.2 ′ 0.2 Ma and 60.2 ′ 0.3 Ma, respectively, indicating that the Red Hills intrusion and mineralization are distinctly older than all other Tertiary magmatism (48-17 Ma) in the Trans-Pecos region of Texas, including the nearby 32 Ma Chinati Mountains caldera. The Red Hills intrusive system is contemporaneous with and genetically related to other Laramide magmatic systems (75-54 Ma) that host porphyry copper deposits in Arizona, southwestern New Mexico, and northern Mexico. These results significantly extend the Laramide magmatic province eastward and suggest that Laramide subduction-related magmatism and deformation are coextensive over a broad area of southwestern North America.

Geochemistry of the Rio Espinharas hybrid complex, northeastern Brazil

The Rio Espinharas pluton, northeastern Brazil, belongs to the shoshonitic series and consists mainly of syenogranite, quartz–monzonite and porphyritic quartz–monzonite, but diorite, quartz–monzodiorite, quartz–syenite and microsyenogranite also occur containing microgranular enclaves, except for the diorite. Most variation diagrams of rocks, amphiboles, biotites and allanites show linear trends, but K, Zr, Sr and Ba of rocks display curved scattered trends. The rocks ranging from diorite to syenogranite define a pseudo-errorchron and have similar REE patterns. Syenogranite and microsyenogranite are derived from two distinct pulses of granite magma with initial 87Sr/ 86Sr ratio of 0.7083±0.0003 and 0.7104±0.0007, respectively. Modelling of major and trace elements shows that the syenogranite evolved by fractional crystallization of plagioclase, microcline, edenite, biotite and titanite, whereas quartz–monzonite, porphyritic quartz–monzonite, quartz–monzodiorite and quartz–syenite resulted from simple mixing between an upper mantle-derived dioritic magma and the upper crust-derived syenogranite magma. Dioritic enclaves are globules of a mafic magma from the upper mantle.

Protolith ages and timing of deformation in the eastern, marginal part of the Sveconorwegian orogen, southwestern Sweden

U–Pb zircon and titanite ages from variably metamorphosed, igneous rocks in the eastern, marginal part of the Sveconorwegian orogen (Eastern Segment), north of lake Vänern, Sweden, suggest that these rocks belong to the younger (c. 1.71–1.65 Ga) igneous suite of the c. 1.85–1.65 Ga Transscandinavian Igneous Belt (TIB). Two porphyritic meta-granites and one isotropic monzonite yield U–Pb zircon ages of 1661±27, 1674±7 and 1674±7 Ma, respectively. These ages support earlier interpretations that the Eastern Segment north of lake Vänern contains tectonically reworked TIB rocks and that there is no major lithological discontinuity either across the Sveconorwegian Frontal Deformation Zone or within the Eastern Segment. Igneous, brown-coloured titanites from five samples yield similar U–Pb ages as the zircons. In contrast, colourless and oblate-shaped titanites from the western, penetratively deformed parts of the Eastern Segment give concordant ages of 976±4 and 956±6 Ma. Further to the east, similar titanite from both a penetratively deformed meta-granite and a ductile shear zone within a porphyritic quartz monzonite are strongly discordant close to late Sveconorwegian lower intercept ages. This type of titanite is interpreted to be syntectonic and formed during the upper greenschist (east)- to amphibolite (west)-facies, fabric-forming event in the Eastern Segment. Since the brown, igneous titanites and the zircons share a common igneous origin, and the single type of metamorphic titanites are either concordant or strongly discordant towards late Sveconorwegian intercept ages, it is inferred that no major tectonothermal event occurred between the time of TIB emplacement and the late Sveconorwegian tectonothermal reworking. Pre-Sveconorwegian, Palaeo- to Mesoproterozoic deformational and metamorphic events (Gothian), which have been inferred west of and further south within the Eastern Segment, appear to be absent in the northern part of this crustal unit.

Geology and geochemistry of the Kokomo mining district, Colorado

The ores of the Kokomo mining district, Colorado, are Ag-Pb-Zn massive sulfide replacement deposits (mantos) controlled by northeast-striking, high-angle faults and hosted by limestone beds in the Pennsylvanian Minturn Formation. The Minturn Formation is as much as 1,830 m thick and consists of interbedded nonmarine, coarse clastic sedimentary rocks and thin marine limestones. The sedimentary section is greatly expanded by Cretaceous-Tertiary porphyritic granodiorite and quartz monzonite sills, dikes, and stocks.Hydrothermal alteration is dominated by skarns in calcareous sedimentary rocks centered on the Tucker Mountain area. Manto orebodies occur to the south in an updip direction distal to the skarns. Intrusive rocks throughout the Kokomo district have been affected by propylitic alteration. Argillic and sericitic alteration of sedimentary and intrusive rocks is restricted to areas immediately around the mantos and along faults that served as conduits for hydrothermal solutions. Mantos are surrounded by halos of siderite-manganosiderite, hydrothermal dolomite, and/or jasperoid in the limestone.Massive sulfide replacement ore exhibits banded and tabular textures very similar to ores at Leadville and Gilman, Colorado. Ore deposition occurred in the general sequence: jasperoid,; iron sulfides (pyrrhotite, marcasite, and pyrite) + siderite, quartz, high iron sphalerite, ferroan dolomite, galena, chalcopyrite and sulfosalts, barite, ferroan calcite, and calcite. Fluid inclusion analyses of quartz and carbonate gangue minerals indicate that temperatures averaged 350 degrees C during the early stages of ore deposition and decreased to about 160 degrees C during the late stages. Ore fluid salinities also decreased through the ore deposition event from 4.6 to 18 O and delta 18 C values compared to diagenetic dolomite due to isotopic exchange between limestones and hydrothermal fluids. Carbonate gangue minerals within the ore zone exhibit lower delta 18 O and delta 13 C values, and these values yield a calculated fluid delta 18 O (sub H 2 O) = 5.0 to 6.9 per mil, within the range for magmatic water. Sulfur isotope values of sulfide minerals range from -0.6 to + 0.8 per mil. The narrow range of delta 34 S values around 0 per mil suggests a magmatic sulfur source.The fission track age of the Kokomo ore system is about 40 Ma. Fission track dates are younger to the north and indicate a thermal center around Tucker Mountain. A porphyritic rhyolite plug on Tucker Mountain, described as a Pennsylvanian volcanic feature in previous literature, yields a fission track age of 39.5 Ma.The Kokomo stable isotope values, fluid inclusion homogenization temperatures, and salinities are comparable to data from other Leadville-type (magmatic hydrothermal) carbonate-hosted sulfide replacement deposits in the Colorado mineral belt, including Leadville and Gilman.