Panzhihua Intrusion Research Articles

Occurrence and enrichment mechanism of Co in Fe-Ti oxide deposits: A case study of the world-class Panzhihua deposit in SW China

The Panzhihua deposit is the one of the largest Fe-Ti oxide deposits in the world and holds 10,000 to 20,000 tons of Co resource with grades varying from 0.01 % to 0.02 %. Detailed field geological investigations and major and trace element analyses, were conducted to reveal occurrence of Co and Ni and their enrichment mechanism. Co and Ni are predominantly enriched in massive magnetite ores (average 277 ppm Co, 281 ppm Ni) of the Lower zone in the Panzhihua intrusion. Co occurs as three types:(1) independent minerals such as cobalt pentlandite (Co3.96-6.98Ni0.85-2.62Fe1.36-2.53S8) and linnaeite (Co1.65-1.88Ni0.99-1.05Fe0.15-0.37S4); (2) isomorphic state substituting for Fe, Ni and/or Mg in pentlandite (Co0.53-0.55Ni4.57-4.65Fe3.80-3.83S8), Co-bearing pyrite (Co0.09-0.12Fe0.89-0.93S2), pyrrhotite (Co 111–1964 ppm), olivine (Co 161–184 ppm), pyrite (Co 3–272 ppm), titanomagnetite (Co 57–181 ppm), ilmenite (Co 57–110 ppm), clinopyroxeneclinopyroxene (Co 34–40 ppm); (3) microscopic sulfide inclusions in chalcopyrite. Sulfide segregation and crystallization are principal mechanisms of Co enrichment. The results offers valuable insights into understanding Co mineralization, resource assessment, and comprehensive utilization in magmatic Fe-Ti oxide deposits.

Formation of layered intrusion: A perspective from vanadium isotopes

Layered intrusions, characterized by their multiple layers, serve as remarkable geological archives of magma evolution in the Earth's crust. However, the magmatic evolution processes that lead to the formation of the chemically diverse layers in the intrusions are still difficult to trace. Here we present V isotope data of whole rocks and mineral separates (clinopyroxene and magnetite) from the Panzhihua layered intrusion in southwest China. The intrusion can be divided into four zones from the base upward: the marginal zone, lower zone, middle zone and upper zone. Both the marginal and upper zones mirror the chemical compositions of the parental magma, with the V isotopic composition being about −0.83‰ ± 0.19‰ (n = 4, 2 s). The lower zone is characterized by Fe-Ti oxide layers, where the whole rocks have a similar V isotopic composition as those of clinopyroxene and magnetite at each depth. The consistency in V isotopic compositions between whole rock and mineral separates reflects the control of silicate liquid immiscibility in forming the Fe-Ti oxide layers. Along the depth profile, whole rocks from the lower zone show limited variations in δ51V values ranging from −0.82‰ to −0.49‰. Such observation reveals the dynamic process of crystallization-mush-immiscibility-layering in charging the generation of repetitive oxide layers. After the formation of the lower zone, the middle zone has a large variation of δ51V values from −0.35‰ to 1.70‰, which can be attributed to fractional crystallization of Fe-Ti oxides. Consequently, the V isotopic signatures indicate that the Panzhihua intrusion was originated from a common basaltic magma and the layering in lower and middle zones resulted from continuous evolution of a single, massive magma unit.

Molybdenum isotopic fractionation in the Panzhihua mafic layered intrusion in the Emeishan large igneous province, southwest China

Abstract The large Mo isotopic fractionations between different geological reservoirs make this isotopic system a potentially useful tool for constraining the origins of magmatism. However, the effect of magmatic differentiation on Mo isotopes is still controversial. In this study, we obtained Mo isotope data for the Panzhihua gabbroic intrusion (i.e., including mineral separates of clinopyroxene, plagioclase, magnetite, and ilmenite). The whole-rock samples and mineral separates exhibit large Mo isotopic fractionations with δ98/95Mo values as follows: magnetite (–0.73‰ to –0.32‰) < clinopyroxene (–0.32‰ to –0.10‰) < ilmenite (0.06‰ to 0.36‰) < plagioclase (0.33‰ to 0.83‰). Iron-Ti oxides have Mo contents that are one order of magnitude higher than those of clinopyroxene and plagioclase. Mass balance calculations based on Mo isotopes and contents are consistent with an accumulated origin for the Panzhihua intrusion. Rayleigh fractionation modeling shows that the removal of magnetite and ilmenite results in significant Mo isotopic fractionation in the residual magma. Due to the low Mo contents of clinopyroxene and plagioclase, Mo isotopes are not significantly fractionated by the removal of these minerals. Therefore, our study highlights that fractionation of Fe-Ti oxides can cause considerable Mo isotopic fractionation; consequently, caution is needed when using Mo isotopes to infer magma origins.

Comment on: Baddeleyite U-Pb age and Hf isotopes, and constraints on genesis of the Panzhihua carbonatite in SW China by Wang et al. (2023)

Wang et al. (2023) propose that rocks adjacent to the Panzhihua intrusion are not marbles and skarns, but carbonatites. If true, this interpretation could have important implications for models explaining the origin of the large Fe-Ti ore deposits in the intrusion. We reject this interpretation for two principal reasons: 1) the objects described as “mantle xenoliths”, and considered, incorrectly, as diagnostic of carbonatite, are in fact deformed and altered mafic/ultramafic intrusions; 2) the concentrations of incompatible trace elements in the marbles are low and typical of metasedimentary rocks, not carbonatite.

Was the Panzhihua Large Fe‐Ti Oxide Deposit (SW China) Formed by Silicate Immiscibility?

AbstractThe Panzhihua mafic intrusion, which hosts a world‐class Fe‐Ti‐V ore deposit, is in the western Emeishan large igneous province, SW China. The formation age (∼260 Ma), Sr, and Nd isotopes indicate that the Panzhihua intrusion is part of the Emeishan large igneous province and has little crustal contamination. However, the ore genesis of the Panzhihua Fe‐Ti‐V ore deposit has been extensively debated. Two different models have been provided to explain the formation of the Panzhihua oxide deposit, namely silicate immiscibility and normal fractional crystallization. Silicate immiscibility occurrings around 1,000 °C at the late stage of basaltic magma evolution argues against the silicate immiscibility model. Apatite‐hosted melt inclusion research indicates that silicate immiscibility occurred at the late stage of Panzhihua magma evolution. However, this may have little potential to form large ore deposits like Panzhihua. However, the continuous compositional variations of the Panzhihua intrusion and the calculations by thermodynamic modelling software support the Panzhihua deposit being formed by normal fractional crystallization. The reciprocal trace element patterns of the Panzhihua intrusion and the nearby felsic rocks also coincide with the fractional crystallization model. Normal fractional crystallization of high‐Ti basaltic magma played a key role in the formation of the Panzhihua Fe‐Ti‐V ore deposit.

Liquid immiscibility in the Panzhihua intrusion, SW China: Evidence from ore textures and Fe–Ti oxide-rich globules in gabbros

Abstract The Panzhihua intrusion hosts a large Fe–Ti oxide deposit in the Permian Emeishan large igneous province (ELIP), SW China. The mechanism of such massive Fe–Ti oxide accumulation in the layered intrusion is still a matter of debate. In this study, we suggest that the ore formation occurred via density-driven liquid segregation of immiscible Fe-rich liquid, instead of simple mineral sorting of Fe–Ti oxides. Interstitial oxides and kinked plagioclase crystals reveal that the Fe–Ti oxides were crystallized in-situ after their surrounding silicate minerals. Dissolution texture of primocryst plagioclase is ubiquitous in the ores, indicating that the primocryst plagioclase grains were in disequilibrium with the surrounding melt. Fe–Ti oxide-rich globules (~38 wt% FeO) are present in the ore-barren gabbro, and likely represent solidified pockets of the immiscible Fe-rich liquid. Olivine in the Fe–Ti oxide ores occurs as primocrysts (avg. Fo = 68.5) that crystalized before the interstitial Fe–Ti oxides, or as growth rims (avg. Fo = 77.5) that crystalized after interstitial Fe–Ti oxides. The primocryst olivine was likely in equilibrium with the Panzhihua parental magma, and its composition matches well with that of the basalt (Fe2O3T = ~16 wt%) exposed near the intrusion. The olivine rim was likely in equilibrium with the residual melt produced from ~33% crystallization of the Fe–Ti oxide-rich globule. This study confirms that the ore layers are formed by the sinking of dense immiscible Fe-rich liquid to squeeze out the original silicate melt in the crystal mush, forming the (semi-)massive Fe–Ti oxide layered ores.

Nano-Micron Exsolved Spinels in Titanomagnetite and Their Implications for the Formation of the Panzhihua Fe-Ti-V Oxide Deposit, Southwest China.

The nano-micron exsolved spinels with various mineralogical characteristics in titanomagnetite from Fe-Ti oxide gabbros in the Panzhihua Fe-Ti-V oxide deposit, SW China, have been studied by field emission scanning electron microscopy (FE-SEM) and electron probe microanalysis (EPMA) based on comparisons of physical and chemical conditions at different stratigraphic heights to investigate the compositional inheritance between titanomagnetite and exsolved spinel and further explore the relationship between the morphology and growth of exsolved spinels. Restored chemical data for titanomagnetite combined with evidence from petrography and whole-rock geochemistry imply fractional crystallization of the Panzhihua Fe-Ti-V oxide deposit, where the titanomagnetite of thick massive oxides at the bottom of the No. VIII orebody represents the early crystallizing phase characterized by high temperature and oxygen fugacity. The chemical variation in the exsolved spinel, which has the same trend as the restored composition of titanomagnetite, represents inheritance from the parent rock within the Panzhihua deposit. Exsolved spinel continuously adjusts morphology and grain size to decrease the total energy of the manganate-spinel system from fine-grained spinels parallel to the {100} plane of titanomagnetite to spinels with complex stellate morphology to bulky granular spinels with high degrees of idiomorphism. The unusual multiple magma replenishment during the mineralizing process and at different stratigraphic heights in the Panzhihua intrusion had an important influence on the thermal evolution history of the orebody, resulting in the identifiable spatial distribution patterns of spinel morphology and grain size. Using spinel exsolution as a discriminator for the provenance of magmatic ore deposits may provide intuitive and easy mineralogical evidence to qualitatively discuss the evolution of the metallogenetic environment and the ore-forming conditions for similar large mafic intrusions.

Sr-Nd-Hf-O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide ore deposits in the Emeishan large igneous province

Magma-carbonate interaction and recycled oceanic crust in the mantle source are thought to have played a critical role in the genesis of magmatic Fe-Ti-V oxide ore deposits in the Emeishan mantle plume-related large igneous province in southwestern China. To test these hypotheses, we have carried out a combined study of zircon Hf-O isotopes and whole-rock Sr-Nd isotopes on three representative magmatic Fe-Ti-V oxide ore deposits associated with different types of wall-rock in the province: the Hongge and Taihe deposits with granitoid wall-rocks in most places, and the Panzhihua deposit with marble wall-rocks. Diopside-garnet marble xenoliths are common in the host gabbros of the Taihe deposit. The zircon separates used in this study are all from the mineralized units of the host layered mafic–ultramafic intrusions. The selected zircon grains yield U-Pb isotopic ages of 258.2 ± 2.8 Ma for Hongge intrusion, 263.3 ± 2.2 Ma for Taihe intrusion, and 257.6 ± 2.1 Ma for Panzhihua intrusion. The Hf-O isotopes of the zircon separates are εHf(t) from 3.1 to 4.7 and δ18O from 5.77 to 6.45‰ for Hongge, εHf(t) from 8.3 to 9.8 and δ18O from 4.12 to 4.56‰ for Taihe, and εHf(t) from 4.6 to 6.3 and δ18O from 5.49 to 6.10‰ for Panzhihua. The zircon δ18O values of the Taihe deposit are significantly lower than the mantle zircon values (5.3 ± 0.3‰), whereas those of the Hongge and Panzhihua deposits are higher than the mantle values. The initial 87Sr/86Sr and εNd(t) of the whole rock samples from the deposits are similar, from 0.7047 to 0.7052 and from 2.3 to 3.1, respectively. The observed decoupling of zircon Hf-O isotopes (low δ18O and high εHf(t) values) in the Taihe deposit is most consistent with a high-temperature altered, low δ18O oceanic gabbroic component in the plume source for this deposit. All of the isotope data together show that the parental magmas for these deposits experienced different types of crustal contamination. Contamination with the Precambrian metamorphic country rocks is much more significant in the parental magma for the Hongge deposit than those for the Panzhihua and Taihe deposits. On the other hand, contamination with marble country rocks is more pronounced in the parental magmas for the Panzhihua and Taihe deposits than in the parental magma for the Hongge deposit. An important new finding from this study is that these deposits are not linked to the same component of the mantle plume nor a single type of crustal contamination.

Iron Isotope Systematics of the Panzhihua Mafic Layered Intrusion Associated With Giant Fe‐Ti Oxide Deposit in the Emeishan Large Igneous Province, SW China

AbstractIn order to investigate how Fe was enriched from parental high‐Ti basaltic magma to form the stratigraphically thick Fe‐Ti oxide ore at the bottom layers, we present a systematic study for Fe isotopic compositions of whole rocks and mineral separates (clinopyroxene, magnetite, and ilmenite) throughout the Panzhihua intrusion. Whole rock δ56Fe ranges from 0 ± 0.02‰ to 0.15 ± 0.04‰, consistent with the range of clinopyroxene (0.01 ± 0.02‰ to 0.16 ± 0.05‰). On the contrary, magnetite (Mt) separates have δ56Fe ranging from 0.17 ± 0.05‰ to 0.62 ± 0.02‰, showing a strikingly complementary trend with coexisting ilmenite (Ilm) separates (−0.52 ± 0.03‰ to −0.09 ± 0.02‰) along the profile. The calculated bulk δ56Fe of Fe‐Ti oxides (Mt + Ilm), however, has a small range from 0.01‰ to 0.16‰, identical to those for clinopyroxene separates and whole rocks. The uniform δ56Fe of clinopyroxene may have resulted from the small Fe isotope fractionation between clinopyroxene and parental magma in early‐stage magma differentiation before substantial crystallization of Fe‐Ti oxides. The complementary trends of δ56Fe for Mt and Ilm along the profile and the uniform bulk δ56Fe of Fe‐Ti oxides are better interpreted as in situ crystallization of Fe‐Ti oxides from the interstitial liquid. Our Fe isotopic data and petrographic observations indicate that the thick Fe‐Ti oxide ore layers in the lower zone of the Panzhihua intrusion may be attributed to in situ crystallization of Mt and Ilm from the interstitial, immiscible Fe‐rich melt in the lower part of the magma chamber.

Mineralogical Characteristics of Exsolved Spinel in the Panzhihua V‐Ti Magnetite Deposit, Sichuan: Implications for the Mineralization Process

AbstractSpinel exsolution is widespread in titanomagnetite from the Fe‐Ti oxide gabbro of the Panzhihua intrusion, Emeishan Large Igneous Province, SW China. However, little research has been conducted into the implications of patterns in the mineralogical characteristics of the spinel for spatial variation in the controls on the exsolution mechanism and, hence, the formation process of the ore deposit. This study selected the Lanjiahuoshan Ore Block in the Panzhihua V‐Ti magnetite deposit to explore this issue, systematically studying exsolution textures in the titanomagnetite through petrographic observation and the integrated use of in‐situ microanalysis. The results show that the exsolved spinel gradually becomes finer‐grained and less abundant from the center to edge and the bottom to top of the ore bodies. Compositionally, there is an inverse correlation between the size of exsolved spinel grains and their Mg# value. In addition, there is compositional zonation in the spinel interiors, with a gradual increase in the Mg content and decrease in Fe content from the core to the rim. The analysis suggests that fractional crystallization of ferrotitanium magma with a high oxygen fugacity in a shallow magma chamber caused compositional differences in the primary magnetite solid solution in different parts of the Panzhihua intrusion. Additionally, the thermal evolution of the magnetite solid solution differed in different parts of orebody, bringing about variations in spinel development. Together, these effects resulted in spatial variation in the abundance, grain size, and morphology of spinel in different parts of the orebody and intrusion that follows an identifiable distribution law. Furthermore, the compositional zonation of exsolved spinels reflects the rapid growth of exsolution features in a high‐temperature environment. Thus, the size, morphology, abundance, and composition of spinel exsolution features in titanomagnetite provide a valuable petrogenetic tool for estimating the maturity and formational environment of the deposit.

The genesis of the newly discovered giant Wuben magmatic Fe–Ti oxide deposit in the Emeishan Large Igneous Province: a product of the late-stage redistribution and sorting of crystal slurries

A giant Fe–Ti oxide deposit hosted by the Wuben mafic intrusion has recently been discovered in the Pan–Xi area of the Emeishan Large Igneous Province (ELIP). The evolved compositions of the gangue minerals within the Fe–Ti oxide ores indicate that they formed during later stages of magma differentiation than those within the neighboring Panzhihua intrusion or other ore-bearing intrusions in this area. The rocks from the Wuben intrusion and MZb of the Panzhihua intrusion contain compositionally similar silicate minerals and have similar titanomagnetite/ilmenite ratios, suggesting that the former is related to and probably connected to the latter by subsurface magmatic conduits. This indicates that unconsolidated minerals that formed in the MZb flowed as crystal slurries into the Wuben magma chamber during the later stages of evolution of the parental magma. The later secondary enrichment of Fe–Ti oxides by mechanical redistribution and the sorting of crystals as a result of density and size differences generated the Wuben massive Fe–Ti oxide bodies. The ilmenite was commonly saturated in the magma at late stage of differentiation in the ELIP, thereby the associated deposit contains much higher contents of ilmenite. This indicates that future exploration for Fe–Ti oxide mineralization in the ELIP should not merely focus on the lower parts of large layered intrusions but should also include nearby relatively small intrusions or even the upper parts of large intrusions, especially as ilmenite-enriched Fe–Ti oxide deposits may have greater economic value than ilmenite-poor deposits.

Petrography and trace element signatures in silicates and Fe–Ti-oxides from the Lanjiahuoshan deposit, Panzhihua layered intrusion, Southwest China

Permian mafic–ultramafic layered intrusions in the central part of the Emeishan Large Igneous Province (ELIP), Southwestern China, host Fe–Ti–V-oxide ores that have features which distinguish them from other large layered intrusion-hosted deposits. The origin of these ores is highly debated. Careful petrographic examination, whole rock analysis, electron probe microanalysis, and measurement and mapping of trace element concentrations by laser ablation inductively coupled plasma mass spectrometry in all major and minor minerals (clinopyroxene, plagioclase, olivine, amphibole, titanomagnetite, ilmenite, pleonaste and pyrrhotite) has been undertaken on samples from the Lanjiahuoshan deposit, representing the Middle, Lower and Marginal Zone of the Panzhihua intrusion. Features are documented that impact on interpretation of intrusion petrology and with implications for genesis of the Fe–Ti–V-oxide ores. Firstly, there is evidence, as symplectites between clinopyroxene and plagioclase, for introduction of complex secondary melts. Secondly, reaction between a late hydrothermal fluid and clinopyroxene is recognized, which has led to formation of hydrated minerals (pargasite, phlogopite), as well as a potassium metasomatic event, postdating intrusion solidification, which led to formation of K-feldspar. Lastly, partitioning of trace elements between titanomagnetite and silicates needs to consider scavenging of metals by ilmenite (Mn, Sc, Zr, Nb, Sn, Hf and Ta) and sulfides, as well as the marked partitioning of Co, Ni, Zn, Ga, As and Sb into spinels exsolved from titanomagnetite. The role of these less abundant phases may have been understated in previous studies, highlighting the importance of petrographic examination of complex silicate–oxide–sulfide assemblages, as well as the need for a holistic approach to trace element analysis, acknowledging all minerals within the assemblage.

Controls on trace-element partitioning among co-crystallizing minerals: Evidence from the Panzhihua layered intrusion, SW China

The factors and processes that control trace-element partitioning among co-crystallizing cumulus minerals in layered intrusions have long been controversial. Here we address this issue using new laser ablation ICP-MS trace element data for magnetite, ilmenite, and clinopyroxene from the Panzhihua layered intrusion in the Emeishan large igneous province, SW China. The cumulus minerals display strong Ni, Co, and Cr depletions, indicative of parental magmas low in concentration of these elements probably due to prior sulfide removal and the fractionation of chromite or Cr-magnetite in a staging magma chamber at depth. Both magnetite and clinopyroxene show cyclical variations in some transition elements (e.g., Cr, V, and Ni) along the stratigraphic section. The average concentrations of these transition elements in magnetite are positively correlated with those in clinopyroxene, likely resulting from co-crystallization of magnetite and clinopyroxene. The incompatible element (e.g., Zr, Hf, and Nb) concentrations of the cumulus minerals from the Lower Zone are highly variable compared to those of the Middle and Upper Zones. These large variations in trace element compositions are attributed to a “trapped liquid shift” in the Lower Zone. Ilmenite crystals from the Panzhihua intrusion may have undergone extensive modification of transition elements during subsolidus re-equilibration with magnetite, leading to the decoupled variations of transition elements in ilmenite across the Lower Zone stratigraphy. Our study indicates that systematic trace element variations of the main cumulus mineral assemblage, rather than a single mineral, need to be considered to better constrain the magmatic differentiation and elemental fractionation of layered intrusions.

Apatite geochemistry of the Taihe layered intrusion, SW China: Implications for the magmatic differentiation and the origin of apatite-rich Fe-Ti oxide ores

The Taihe intrusion is one of the layered intrusions situated in the central zone of the Emeishan Large Igneous Province (ELIP), SW China. The cyclic units in the Middle Zone of the intrusion are composed of apatite-magnetite clinopyroxenite at the base and gabbro at the top. The apatite-rich oxide ores contain 6–12modal% apatite and 20–50modal% Fe-Ti oxides evidently distinguished from the coeval intrusions in which apatite-rich rocks are poor in Fe-Ti oxides. Most of apatites of the Taihe Middle and Upper Zones are fluorapatite, although four samples show slightly high Cl content in apatite suggesting that they crystallize from a hydrous parental magma. Compared to the apatite from the gabbro of the Panzhihua intrusion, situated 100km to the south of the Taihe intrusion, the apatite of the Taihe rocks is richer in Sr and depleted in HREE relative to LREE. The calculated magma in equilibrium with apatite of the Taihe Middle and Upper Zones also shows weakly negative Sr anomalies in primitive mantle normalized trace element diagrams. These features indicate that the apatite of the Taihe Middle and Upper Zones crystallizes after clinopyroxene and before plagioclase. The apatite of the Taihe Middle and Upper Zones shows weakly negative Eu anomalies suggesting a high oxygen fugacity condition. The high iron and titanium contents in the oxidizing magma result in crystallization of Fe-Ti oxides. Crystallization of abundant Fe-Ti oxides and clinopyroxenes lowers the solubility of phosphorus and elevates SiO2 concentration in the magma triggering the saturation of apatite. The positive correlations of Sr, V, total REE contents and Ce/Yb ratio in apatite with cumulus clinopyroxene demonstrate approximately compositional equilibrium between these phases suggesting they crystallized from the same ferrobasaltic magma. Early crystallization and accumulation of Fe-Ti oxide together with apatite produced the apatite-rich oxide ores at the base of the cyclic units of the Taihe Middle Zone.

Integrated O–Sr–Nd isotope constraints on the evolution of four important Fe–Ti oxide ore-bearing mafic–ultramafic intrusions in the Emeishan large igneous province, SW China

In the Emeishan large igneous province, SW China, there are many layered mafic–ultramafic intrusions such as the Baima, Hongge, Panzhihua and Taihe intrusions that host world-class Fe–Ti oxide ore deposits. Despite numerous studies, the origin of these deposits still remains elusive. This includes the role of crustal contamination, especially addition of external CO2 from carbonate country rocks during contact metamorphism, in triggering Fe–Ti oxide crystallization from high-Mg basaltic magma. To address this important issue, we have carried out an integrated O–Sr–Nd isotope study of these ore-bearing intrusions and the country rocks. Our results show that in these intrusions clinopyroxene is much less susceptible to fluid–mineral oxygen isotope exchange than coexisting plagioclase and Fe–Ti oxides, which is similar to other intrusions worldwide (e.g., Taylor, 1967; Gregory and Taylor, 1981). Our calculations based on the least exchanged clinopyroxene oxygen isotope data show that the mean δ18O values for the parental magmas of these intrusions are Baima=5.7‰, Panzhihua=6.1‰, Taihe=5.9‰. The estimated mean δ18O value for the parental magma of the Upper and Middle Zones of the Hongge intrusion is 6.2‰, which is similar to those for the parental magmas of the other intrusions (Baima, Panzhihua and Taihe). By contrast, the estimated mean δ18O value for the parental magma of the Lower Zone of the Hongge intrusion is higher (6.9‰). This difference, together with higher initial 87Sr/86Sr ratios (0.7057 to 0.7076) and lower εNdt values (−2.82 to −0.07) for this zone, can be attributed to higher degrees of contamination with siliceous crustal materials in this zone than elsewhere in this intrusion. Comparison of O–Sr–Nd isotope compositions between the intrusions and country rocks reveals that bulk assimilation of carbonate country rocks is negligible in all of these intrusions. Mixing calculations using the O–Sr–Nd isotope data are consistent with variable degrees of contamination with siliceous crustal materials in the intrusions: Panzhihua, <5%, Baima and Taihe, <10%, the Middle and Upper Zone of the Hongge intrusion, <10%, the Lower Zone of the Hongge intrusion, <15%. These percentages are maximum values and may be reduced if contamination was selective in nature, involving Sr- and Nd-bearing fluids or partial melts. Based on the oxygen isotope results, an iterative calculation with a CO2/magma mass ratio=1/1000 for each increment reveals that the Panzhihua magma reacted with <1wt.% of CO2 released from the footwall during contact metamorphism. This amount is not sufficient to increase the oxidation state of the magma to the level that Fe–Ti oxides would crystallize alone from the magma. Therefore, we conclude that external CO2 did not play a major role in the formation of the Fe–Ti oxide ores in the Panzhihua intrusion.

CONTRASTING PARENTAL MAGMA COMPOSITIONS FOR THE HONGGE AND PANZHIHUA MAGMATIC Fe-Ti-V OXIDE DEPOSITS, EMEISHAN LARGE IGNEOUS PROVINCE, SW CHINA

Research Article| September 01, 2014 CONTRASTING PARENTAL MAGMA COMPOSITIONS FOR THE HONGGE AND PANZHIHUA MAGMATIC Fe-Ti-V OXIDE DEPOSITS, EMEISHAN LARGE IGNEOUS PROVINCE, SW CHINA* Zhong-Jie Bai; Zhong-Jie Bai 1State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China Search for other works by this author on: GSW Google Scholar Hong Zhong; Hong Zhong † 1State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China †Corresponding author: e-mail, zhonghong@vip.gyig.ac.cn Search for other works by this author on: GSW Google Scholar Chusi Li; Chusi Li 2Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405 Search for other works by this author on: GSW Google Scholar Wei-Guang Zhu; Wei-Guang Zhu 1State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China Search for other works by this author on: GSW Google Scholar De-Feng He; De-Feng He 1State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China Search for other works by this author on: GSW Google Scholar Liang Qi Liang Qi 1State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China Search for other works by this author on: GSW Google Scholar Economic Geology (2014) 109 (6): 1763–1785. https://doi.org/10.2113/econgeo.109.6.1763 Article history received: 29 Jul 2013 accepted: 03 Jan 2014 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Zhong-Jie Bai, Hong Zhong, Chusi Li, Wei-Guang Zhu, De-Feng He, Liang Qi; CONTRASTING PARENTAL MAGMA COMPOSITIONS FOR THE HONGGE AND PANZHIHUA MAGMATIC Fe-Ti-V OXIDE DEPOSITS, EMEISHAN LARGE IGNEOUS PROVINCE, SW CHINA. Economic Geology 2014;; 109 (6): 1763–1785. doi: https://doi.org/10.2113/econgeo.109.6.1763 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract Many ~260 Ma mafic-ultramafic layered intrusions, including Hongge and Panzhihua, in the Emeishan large igneous province, southwestern China host world-class Fe-Ti-V oxide ore deposits. These two most important ore-bearing intrusions show differences in lithology and mineral chemistry. The most important orebodies in the Hongge intrusion occur as concordant layers in the middle part of the intrusion, closely associated with clinopyroxenites. Titanomagnetite and Mg-rich ilmenite are the major ore minerals of the Hongge deposit. Coexisting clinopyroxene contains >1.7 wt % TiO2. These data indicate high Ti parental magma for the Hongge ore-bearing clinopyroxenites. In the Panzhihua intrusion, the most important orebodies also occur as concordant layers but in its lower part instead of middle part. In contrast with the Hongge deposit, the most important host rocks of the Panzhihua deposit are gabbros, not clinopyroxenites. In addition, ilmenite is rare and titanomagnetite is predominant in the Panzhihua deposit. Coexisting clinopyroxene in the Panzhihua deposit contains <1.6 wt % TiO2. The contrasting lithologic and mineral compositions indicate that the parental magma for the Hongge deposit has higher TiO2 than that for the Panzhihua deposit. The compositions of clinopyroxene from the Panzhihua and Hongge deposits indicate that their parental magmas are also different in MgO/FeO and trace element ratios as well. Calculations using average experimental Mg-Fe exchange coefficient and trace element partition coefficients between clinopyroxene and magma show that the Hongge parental magma has higher MgO/FeO ratios and more fractionated mantle-normalized trace element patterns than the Panzhihua parental magma. The estimated compositions of the parental magmas for the Hongge and Panzhihua ore-bearing lithologies resemble the average compositions of the Longzhoushan-type high Ti basalts and Ertan-type intermediate Ti basalts in the Emeishan large igneous province, respectively. The new trace element data from this study, together with available Sr-Nd isotope data for the ore-bearing intrusions from literature, support a new petrogenetic model involving selective assimilation of newly subducted, stagnant oceanic gabbroic slab above the deep-seated Emeishan mantle plume. This process and subsequent contamination with the upper crust played an important role in the variation of parental magma compositions between the Hongge and Panzhihua magmatic oxide ore deposits. Abundant Fe-Ti oxide ore deposits associated with less evolved basaltic magma in the Emeishan large igneous province than elsewhere in the world are attributed to selective assimilation of newly subducted, stagnant oceanic lithospheric slab by the ascending mantle plume-derived picritic magma that was originally undersaturated with Fe-Ti oxides. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Timescale of emplacement of the Panzhihua gabbroic layered intrusion recorded in giant plagioclase at Sichuan Province, SW China

Abstract Giant plagioclase crystals carried into the Panzhihua gabbroic layered intrusion from a deeper magma chamber can help constrain the timescales of emplacement of the Panzhihua intrusion in the Emeishan large igneous province (LIP). In this study, we present the petrographic textures and chemical compositions of giant plagioclase and fine-grained gabbro samples along a ~ 50 m horizontal outcrop of the low zone of the Panzhihua deposit. The giant plagioclase gabbro (GPG) dykes mostly intrude into the fine-grained gabbros without significant contact. Both types of gabbros have the similar bulk-rock major and trace element compositions. However, the mineral composition shows that most of the plagioclase megacrysts contain less An than the plagioclase in fine-grained gabbro samples. In situ analyses of Sr isotopes from core-to-rim transects of plagioclase megacrysts are constant, indicating that there are no recycled crystals. The textural characteristics of samples combined with petrological modeling using MELTS suggest that the plagioclase megacrysts should crystallize and grow in a deeper magma chamber. Textual studies of the GPG indicate that these plagioclase megacrysts mostly plot as straight lines on a classic crystal size distribution (CSD) diagram. For a plagioclase growth range of 10 − 11 –10 − 10 mm/s, the plagioclase should have a growth time of 530–8118 years. In a 100 km 3 magma chamber releasing thermal energy at a rate of 1000 MW, the Panzhihua intrusion should reach 50% crystallization after ~ 2400 years. The growth time recorded by the megacrysts in the GPG and numerical modeling may indicate that the emplacement and crystallization of the Panzhihua intrusion may have taken place in thousands of years. In the Emeishan LIP, therefore the combination of large volumes of Fe-rich magma flux and efficient metal precipitation led to the formation of a giant Fe–Ti–V oxide deposit in a short period.

Trace element compositions of apatite from the middle zone of the Panzhihua layered intrusion, SW China: Insights into the differentiation of a P- and Si-rich melt

Abstract The Panzhihua layered intrusion in the ~ 260 Ma Emeishan large igneous province is composed of melagabbro and Fe–Ti oxide ore bodies in the lower zone (LZ) and the lower part of the middle zone (MZa), and Fe–Ti oxide-poor leucogabbro in the upper part of the middle zone (MZb) and upper zone (UZ). Cumulus apatite grains occur in the ~ 500- to 600-m-thick MZb, which makes up 25–30% of the ~ 2-km-thick intrusion. Apatite grains from the MZb show two compositional reversals in the composition of Sr, which divide the MZb into three sub-units from the base upwards, MZb1, MZb2 and MZb3. There is 1–3 vol.% apatite in the MZb1 and MZb2 and 2–5 vol.% apatite in the MZb3. Both apatite and plagioclase have an overall trend of decreasing Sr in each sub-unit. Most apatite grains from the MZb1 and MZb2 have negative Eu anomalies (Eu/Eu* = 0.70–0.98) on chondrite-normalized REE plots and some at the top of the MZb2 have positive Eu anomalies (Eu/Eu* = 1.09–1.18), whereas all grains from the MZb3 have positive Eu anomalies (Eu/Eu* = 1.11–1.25). We consider that the Panzhihua intrusion formed due to immiscibility of ferrobasaltic magmas in a large convection cell at high temperatures. The immiscible Fe-rich melt tended to move towards the base of the chamber, whereas the Si-rich melt moved upwards due to density differences. Crystallization of Fe–Ti oxides from the Fe-rich melt at high temperatures may result in the enrichment of P in the residual magmas. The upward moving residual P-rich magmas may have mixed with Si-rich melt to form a P- and Si-rich melt in the upper part of the chamber, from which the MZb formed. Double-diffusive convection circulated in the P- and Si-rich melt to form stratified magma layers. Magma mixing between the stratified magma layers resulted in the compositional reversals of apatite along the boundaries. Negative Eu anomaly of apatite in the MZb1 and MZb2 is attributed to prior crystallization of plagioclase, whereas replenishment of a syenitic magma to the MZb3 may result in the positive Eu anomaly of apatite in the MZb3. The immiscibility model can explain why the apatite-rich MZb is above the major Fe–Ti oxide layers in the Panzhihua intrusion.

Trace element, PGE, and Sr–Nd isotope geochemistry of the Panzhihua mafic layered intrusion, SW China: Constraints on ore-forming processes and evolution of parent magma at depth in a plumbing-system

The Panzhihua intrusion (260Ma) is part of the Emeishan Large Igneous Province (ELIP), SW China. Layered intrusions related to the ELIP have recently received much attention due to their economic potential for Ni–Cu–PGE and Fe–Ti oxide ore deposits. ELIP layered intrusions vary in composition from ultramafic to mafic, which are interpreted to have crystallised from two distinct magma series through plume-related partial melting of the mantle: (1) high-Ti basalt and (2) low-Ti basalt.We present here new trace element, PGE, and Sr–Nd isotope data for the Panzhihua intrusion in order to constrain the evolution of the parent magma from source to current chamber. REE profiles are generally characterised by flat LREE profiles with low (La/Sm)N<2 and steeper HREE with (Gd/Yb)N – general<2.5. Primitive mantle-normalised trace element profiles are characterised by negative Th–U, La–Ce and Zr–Hf anomalies. The Panzhihua intrusion is PGE-depleted relative to related volcanic rocks, with total PGE concentrations generally≪5ppb. Cu/Pd (24,000–250,000) and Pd/Pt (0.3–8.3). (87Sr/86Sr)i and εNdi value ranges are 0.7043–0.7054 and −0.61–3.71 respectively with distinct enriched values for marginal zone rocks.The Panzhihua magma is likely related to a picritic parent magma. Sr–Nd isotope data indicate a common source for the gabbroic and Fe–Ti oxide ore rocks with only minor or localised crustal contamination. The highly PGE-depleted and elevated Cu/Pd nature of the Panzhihua rocks suggests early segregation of a sulphide liquid. Positive correlation of Cr and Ni with MgO suggest fractionation of olivine and chromite. Enriched Sr–Nd isotopic ratios indicate a proportion of assimilation of crustal material at depth, which would aid S-saturation. S-saturation was likely caused by a combination of fractional crystallisation and assimilation of crustal material. Modelled fractionation of picritic parent magma, using Pt, Pd and Cr indicate that approximately 25% fractional crystallisation of 96% olivine, 4% chromite and 0.15% sulphide is required to produce the PGE and Cr depletion observed.The Panzhihua intrusion represents a feeder/plumbing system related to ELIP volcanism. Picritic magmas fractionate at depth forming the parental basaltic magmas of the Panzhihua intrusion. Furthermore, the main Fe–Ti oxide ore layer, within the section of the intrusion, is not in situ and interpreted to be emplaced along the footwall contact as a result of gravitational instability and slumping of crystal-rich slurries.

Hydration vs. oxidation: Modelling implications for Fe–Ti oxide crystallisation in mafic intrusions, with specific reference to the Panzhihua intrusion, SW China

Recent work on the Panzhihua intrusion has produced two separate models for the crystallisation of the intrusion: (1) low-Ti, high CaO and low H2O (0.5 wt.%) parent magma (equivalent to Emeishan low-Ti basalt) at FMQ; and (2) high-Ti, low CaO and higher H2O (>1.5 wt.%) parent magma (equivalent to Emeishan high-Ti basalt) at FMQ + 1.5. Modelling of these parent magma compositions produces significantly different results.We present here detailed f(O2) and H2O modelling for average compositions of both Emeishan high-Ti and low-Ti ferrobasalts in order to constrain the effects on crystallisation sequences for Emeishan ultramafic–mafic layered intrusions. Modelling is consistent with numerous experimental studies on ferrobasaltic magmas from other localities (e.g. Skaergaard intrusion). Modelling is compared with the geology of the Panzhihua intrusion in order to constrain the crystallisation of the gabbroic rocks and the Fe–Ti oxides ore layers. We suggest that the gabbroic rocks at the Panzhihua intrusion can be best explained by crystallisation from a parent magma similar to that of the high-Ti Emeishan basalt at moderate H2O contents (0.5–1 wt.%) but at the lower end of TiO2 content for typical high-Ti basalts (2.5 wt.% TiO2). Distinct silicate disequilibrium textures in the Fe–Ti oxide ore layers suggest that an influx of H2O may be responsible for changing the crystallisation path. An increase in H2O during crystallisation of gabbroic rocks will result in the depression of silicate liquidus temperatures and resultant disequilibrium with the liquid. Continued cooling of the magma with high H2O then results in precipitation of Mt–Uv alone.The H2O content of parent magmas for mafic layered intrusions associated with the ELIP is an important variable. H2O alters the crystallisation sequence of the basaltic magmas so that at high H2O and f(O2) Mt–Uv crystallises earlier than plagioclase and clinopyroxene. Furthermore, the addition of H2O to an anhydrous magma can explain silicate disequilibrium texture observed in the Fe–Ti oxide ore layers.