Fe-Ti Oxide Deposits 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.

Apatite trace elements and O-Sr isotopes reveal different magmatic sources of Fe-Ti oxide deposits in the eastern Tianshan, NW China

Magmatic Fe-Ti oxide deposits are one of the most important iron deposit in eastern Tianshan, NW China, and their ore-forming mechanism remains obscure. Here, we use trace elements and O-Sr isotopes of apatite from two representative magmatic Fe-Ti oxide deposits (Niumaoquan and Weiya) in the eastern Tianshan to constrain the genesis of ore formation. The apatites from the Niumaoquan Fe-Ti oxide ores exhibit higher Eu/Eu* values, lower Mn contents, and larger REE variations than those from the Weiya Fe-Ti oxide ores, indicating a protracted evolution process of the Niumaoquan ore-forming magmas under a relatively reduced condition. Specifically, the apatites from the Niumaoquan Fe-Ti oxide ores can be divided into two groups: Group 1 with relatively low REE contents, low 87Sr/86Sr ratios (0.70574–0.70641) and high δ18O values (5.1–5.6‰), and Group 2 with relatively high REE contents, high 87Sr/86Sr ratios (0.70703–0.70792) and low δ18O values (2.8–3.3‰). The Group 1 apatites formed by early crystallization in the mantle, while the Group 2 apatites formed by assimilation of low δ18O-high 87Sr/86Sr altered rocks during magmas emplacement en route to the continental crust. Unlike the Niumaoquan apatites, the apatites from the Weiya Fe-Ti oxide ores have relatively homogeneous, high δ18O values (8.3‰-9.1‰) and 87Sr/86Sr ratios (0.70798–0.70848), indicating involvement of continental crustal materials in their mantle sources. Combined with previous studies, we suggest that the Niumaoquan and the Weiya Fe-Ti oxide deposits formed in a non-plume tectonic setting but they originated from different magmatic sources. Our study highlights that trace elements and O-Sr isotopes of apatite can be used as powerful tools to constrain the source characteristics and ore-forming processes of magmatic Fe-Ti oxide deposits.

Formation of Fe-Ti oxide and Ni-Co sulfide ores by concentric tube flow and hydrous metal-rich melt recharge into the cooling crystal mush: Example from the Hongge intrusion in Panxi region, SW China

The Panxi (ultra-)mafic intrusions are relatively small compared with world-class ore-related (ultra-)mafic intrusions, but they host several super-large Fe-Ti oxide deposits and few small Cu-Ni (PGE) sulfide deposits. The mechanisms that concentrate huge amounts of oxide minerals into these small intrusions and form the distinct oxide and sulfide mineralization remain poorly understood. Here, we investigate the magma dynamics that produced extensive Fe-Ti oxide and coexisting Ni-Co sulfide mineralization in the Hongge intrusion of Panxi region, based on detailed field cross-cutting relations and petrographic observations, bulk-ore/rock geochemistry, and in-situ LA-ICP-MS magnetite trace element analyses. The Fe-Ti oxide ores include magnetite-poor (<60 vol%) disseminated and magnetite-rich (>60 vol%) massive types, with the former further divided into the gabbro-hosted (GH) and (olivine-)pyroxenite-hosted (OPH) subtypes. The GH oxide ores have Cr-poor (median 86.9 ppm) magnetite and abundant apatite interstitial to silicate minerals. In contrast, the OPH and massive oxide ores have Cr-rich (median 13,956 ppm) magnetite that envelops resorbed silicate minerals. Principal component analyses of bulk-ore and magnetite elemental contents reveal genetic links between the OPH and massive oxide ores, but remarkable genetic distinction from the GH oxide ores. Considering the overall lopolith-shape orebody geometry of several branch intrusions, the GH oxide ore formation may have involved spontaneous development of concentric tube flow zones within the cooling crystal mush. However, the lower P but much higher Cr-Cu-Co-Ni contents than the GH oxide ores and the sharp intrusion of massive oxide ores into the OPH oxide ores suggests that the OPH and massive oxide ores were probably formed by upward percolation and later intrusion of hydrous Fe-rich melts from a deep-seated magma reservoir into semi-solidified and fossilized mush, respectively. In addition, sulfide ores occur mainly as irregular/lenticular aggregates in massive oxide ores and are depleted in Cu and platinum group elements (PGEs), indicating early, deep-level sulfide segregation that scavenged the Cu and PGEs from the magmas. Hence, we envisage that the assimilation of S-deficient wall-rocks into basaltic magmas may have induced the early sulfide saturation and retain the majority of Fe for later precipitation as principal oxide and minor PGE-Cu-depleted sulfide ores.

Open-system differentiation of mafic magmas before the formation of layered Fe-Ti(V) deposits in Southeast China

Mafic magmatic differentiation is an important mechanism to drive Fe-Ti enrichments in melt and final formation of layered Fe-Ti-(V) oxide deposits, but how the differentiation operates and how the state of magmatic reservoirs controls differential metallogenic potential are unclear. The Xialan magmatic complex in northern Guangdong Province is the only complex hosting layered Fe-Ti (V) deposits in Southeast China and the formation of such oxide deposits is not addressed in detail. Here, we present an integrated study of geochronology, mineral geochemistry, whole-rock major and trace elements, as well as Sr-Nd-Pb isotopes, on the mafic rocks associated with the Xialan layered Fe-Ti (V) oxide deposits. The investigated mafic rocks are cogenetic and can be classified into three types according to field and textural features: diabase, Fe-Ti rich gabbro, and Fe-Ti barren gabbro. Based on petrographic observation and major and trace element geochemistry, the gabbros and diabases represent cumulates and residual melts, respectively. However, the Fe-Ti rich gabbros show different Nd isotopes from the other rocks, which indicates an open-system differentiation for the Xialan parental magma. A two-stage evolution process for the Xialan parental magma before the final crystallization fractionation to form the oxide deposits is further proposed based on MELTs modeling results and the characters of mineral assemblages. At the early stage, the magmas started differentiation with 0.5 wt% initial H2O content and moderate oxygen fugacity (△FMQ = ca. + 0.5 – +1.5) at 5 kbar and generated Fe-Ti enriched melts. At the later stage, the Fe-Ti rich melts gradually evolved to a much higher H2O content (>3 wt%), which stabilized the Fe-Ti oxides and hornblendes. Wall-rock assimilation during the late-stage magma evolution is suggested to be the key factor to elevate the H2O contents and oxygen fugacity of the magma which finally produced the layered Fe-Ti oxides. As such, this study demonstrates that open-system differentiation of mafic magmas can play a key role in the final generation of some hornblende-bearing layered Fe-Ti oxide deposits.

Characterizing a new type of nelsonite recognized in the Damiao anorthosite complex, North China Craton, with implications for the genesis of giant magmatic Fe-Ti oxide deposits

Abstract Nelsonite (Fe-Ti oxide-apatite rock) devoid of silicates offers a rare opportunity to investigate the magma processes for the formation of magmatic Fe-Ti oxide deposits. Both fractional crystallization and silicate liquid immiscibility have been put forward, but the lack of robust evidence has hindered unambiguously distinguishing the role of these two processes in Fe-Ti mineralization. The nelsonite and associated Fe-Ti-P-rich rocks hosted in the Proterozoic Damiao anorthosite complex represent a typical example for studying Fe-Ti ore-forming processes. We recognized a new type of nelsonite (type-I) in the Damiao complex, which is distinct from the two known types of nelsonite (type-II and type-III) from the same complex. The type-I nelsonite is characterized by its coexistence with oxide-apatite gabbronorite and granite in the same dike, and all these rocks have identical emplacement ages (1740 ± 7 Ma), subparallel REE patterns, and major-element compositions lacking intermediate compositions, suggesting derivation from conjugate Fe- and Si-rich melts generated by silicate liquid immiscibility. The large type-II nelsonite bodies form irregular dikes along fractures in anorthosite and constitute the major ore type. The type-III nelsonite occurs as conformable layers or pods within oxide-apatite gabbronorite and pyroxenite, and occupies the end part of the type-II dike. The latter two types of nelsonites formed by extensive fractional crystallization of residual magma with crystal accumulation and subsequent hydrothermal replacement. During residual magma evolution, silicate liquid immiscibility was crucial for Fe-Ti-P enrichment, fractional crystallization was responsible for enhancing oxide-apatite concentrations, and hydrothermal replacement was effective for mobilizing oxide-apatite concentrations. Our newly recognized nelsonite provides an unambiguous, outcrop-scale, field evidence for the operation of silicate liquid immiscibility process. We show that giant magmatic Fe-Ti oxide orebodies can form by a combination of processes involving silicate liquid immiscibility, fractional crystallization and hydrothermal mobilization.

In-situ trace elements and Fe isotope compositions of magnetite in Gwanin Fe-Ti oxide deposit, South Korea

In-situ trace elements and Fe isotope compositions of magnetite in Gwanin Fe-Ti oxide deposit, South Korea

Integrating mineralogy, geochemistry and aeromagnetic data for detecting Fe–Ti ore deposits bearing layered mafic intrusion, Akab El-Negum, Eastern Desert, Egypt

This study delineated the Fe–Ti oxide deposit concurrencies on the layered mafic intrusion in Gabal Akab El-Negum (GAN), South Eastern Desert, Egypt, using aeromagnetic mapping and chemical analysis of the hosted mafic rocks and mineralogical studies. Aeromagnetic data was improved using the enhanced horizontal gradient amplitudeto detect the primary structures (edges/contacts/faults) that control the distribution of Fe–Ti ore deposit. GAN layered gabbros are differentiated into troctolite, olivine–, pyroxene–, and hornblende–gabbros. These mafic rocks primarily comprise plagioclase, olivine, pyroxene, and hornblende with Fe–Ti ores (magnetite and ilmenite). The significant variation in Mg# of clinopyroxene between 0.70 and 0.82 indicates the importance of fractional crystallization in developing layered mafic intrusion. Clinopyroxene and plagioclase thermometry yielded low temperatures similar to the fractionated primary basaltic magma. The pairs of magnetite–ilmenite minerals in gabbros provide equilibrium temperatures of 539.44–815.56, and high fO2, reflecting various cooling and subsolidus reequilibration phases of minerals. The enrichment of GAN gabbros in light rare–earth elements relative to heavy rare–earth elements indicates the interaction between the Fe–Ti rich mantle and the fractionated tholeiitic magmas in the back-arc setting, generating Fe–Ti oxide ores.

Contrasting oxidation states of low-Ti and high-Ti magmas control Ni-Cu sulfide and Fe-Ti oxide mineralization in Emeishan Large Igneous Province

Magmatic Ni-Cu-(PGE) sulfide and Fe-Ti oxide deposits in plume-related large igneous provinces (LIPs) are commonly related to low-Ti and high-Ti series magmas, respectively, but the major factors that control such a relationship of metallogenic types and magma compositions are unclear. Magma fO2 controls sulfur status and relative timing of Fe-Ti oxide saturation in mafic magmas, which may help clarify this issue. Taking the Emeishan LIP as a case, we calculated the magma fO2 of the high-Ti and low-Ti picrites based on the olivine-spinel oxygen barometer, and the partitioning of V in olivine. The obtained fO2 of the high-Ti series magma (FMQ + 1.1 to FMQ + 2.6) is higher than that of the low-Ti series magma (FMQ − 0.5 to FMQ + 0.5). The magma fO2 of the high-Ti and low-Ti picrites containing Fo > 90 olivine reveals that the mantle source of the high-Ti series is likely more oxidized than that of the low-Ti series. The results using the ‘lambda REE’ approach show that the high-Ti series may have been derived from relatively oxidized mantle with garnet pyroxenite component. The S contents at sulfide saturation (SCSS) of the two series magmas were calculated based on liquid compositions obtained from the alphaMelts modeling, and the results show that the low-Ti series magma could easily attain the sulfide saturation as it has low fO2 with S being dominantly as S2−. In contrast, the oxidized high-Ti series magma is difficult to attain the sulfide saturation, but could crystallize Fe-Ti oxides at magma MgO content of ∼7.0 wt.%. Thus, contrasting magma fO2 of low-Ti and high-Ti series in plume-related LIPs may play an important role in producing two different styles of metallogeny.

Vanadium removal from mining ditch water using commercial iron products and ferric groundwater treatment residual-based materials

Removal of vanadium from liquid waste streams protects the environment from toxic vanadium species and promotes the recovery of the valuable metal. In this study, real mining ditch water was sampled from a closed vanadium mine (V–Fe–Ti oxide deposit, Finland) and used in sorption experiments at prevailing vanadium concentration (4.66–6.85 mg/L) and pH conditions (7.02–7.83). The high concentration of vanadium in the water represents a potential health concern according to the initial risk assessment carried out in this study. Vanadium was efficiently removed using four different iron sorbents: ferric oxyhydroxide with some goethite (CFH-12), poorly crystallized akaganéite (GEH 101), ferric groundwater treatment residual (GWTR), and GWTR-modified peat (GWTR-Peat). Higher dosage (6 g/L with 24 h contact time) and longer contact time (72 h using 1 g/L dosage) resulted in removal efficiencies of higher than 85%. Kinetic data were well represented by the Elovich model while intra-particle diffusion and Boyd models suggested that the sorption process in a real water matrix was significantly controlled by both film diffusion and intra-particle diffusion. Column studies with CFH-12, GEH 101, and GWTR-Peat showed that the breakthrough started earlier with the mining ditch water compared to a synthetic vanadium solution (investigated only with CFH-12), whereas GEH 101 proved to have the best performance in column mode. The Thomas and Yoon-Nelson column models were found to agree with the experimental data fairly well with the 50% breakthrough time being close to the experimental value for all the studied sorbents.

Petrology and geochemistry of early Permian mafic–ultramafic rocks in the Wajilitag area of the southwestern Tarim Large Igneous Province: Insights into Fe-rich magma of mantle plume activity

The majority of global Fe–Ti-oxide deposits hosted in mafic–ultramafic layered intrusions are closely related to mantle plume activity. The metallogenesis of these Fe–Ti-oxide deposits is still debated, especially with regard to their mantle source and relationship to magmatism. Here we report detailed petrology and geochemistry for early Permian (ca. 280 Ma) mafic–ultramafic igneous rocks in the Wajilitag area of the western Tarim Large Igneous Province (TLIP) to establish the relationships among mantle source, magmatism, and metallogenesis in mantle plume activity. The mafic rocks (i.e., gabbro and diabase) show alkaline affinities and OIB-like trace-element patterns. Clinopyroxenites closely related to Fe–Ti-oxide deposits were derived from the same magmatic system as that of the mafic rocks. The primary magma of the Wajilitag mafic rocks was enriched in FeOT and TiO2 and depleted in SiO2, and has high FC3MS (FeOT/CaO − 3MgO/SiO2) and Fe/Mn, indicating the involvement of Si-poor pyroxenite/eclogite in the mantle source. Primary olivines from the Wajilitag gabbro have consistently high NiO and Fe/Mn. Wajilitag mafic rocks have variable Sr–Nd–Hf isotopes owing to their derivation from a hybrid mantle source with the involvement of subducted oceanic crust and sediments. Subducted slabs within the upper mantle are inferred to have been entrained by the upwelling mantle plume and preferentially melted to produce mainly Fe-rich magma. The occurrence of an adjacent oceanic subduction event just prior to the operation of a mantle plume played a crucial role in the formation of large-scale Fe–Ti-oxide deposits in LIPs.

Large-scale liquid immiscibility in the Hongge layered intrusion hosting a giant Fe-Ti oxide deposit in SW China

The Hongge layered intrusion hosts the largest magmatic Fe-Ti oxide ore deposit in China and provides a valuable opportunity for improving the current understanding of magma differentiation and associated ore-forming processes. In this study, we present geochemical data for apatite- and plagioclase-hosted inclusions in gabbros from the Hongge Upper Zone. The apatite-hosted melt inclusions have a large compositional range with 27.7–60.4 wt% SiO2 and 1.31–25.7 wt% FeOt, which is difficult to be achieved through fractional crystallization but can be well explained by an unmixing process and trapping of immiscible melts along the binodal of a two-liquid field. Only Fe-rich melt inclusions (with 23.8–33.1 wt% SiO2 and 17.7–35.8 wt% FeOt) are observed in plagioclase, which can be attributed to the preferential trapping of immiscible Fe-rich melts by crystallizing plagioclase. The cumulus clinopyroxene and plagioclase display complex zonations with different compositional domains, indicating that disequilibrium crystallization might have happened. We argue that efficient separation of immiscible liquids occurred in the magma chamber and contributed to the concentration of the ore-forming elements Fe and Ti in the remaining immiscible Fe-rich melt. Large amounts of Fe-Ti oxides crystallized from the collected Fe-rich melt forming the major Fe-Ti oxide ore layers of the Hongge intrusion.

Petrogenesis of the gabbronorite sill hosted Fe-Ti oxide ore bodies from the eastern part of Chotanagpur granite Gneissic Complex, India

Magmatic Fe-Ti oxide ore bodies of the eastern Chotanagpur Granite Gneiss Complex (CGGC), India occur as massive conformable lenses within a gabbronorite sill. The occurrence, lithological association, mineralogy, and geochemistry of the Fe-Ti oxide ore bodies are significantly different from the typical Fe-Ti oxide deposits associated with anorthosite complexes and mafic- ultramafic complexes. Textural evidence and mineral chemistry suggest mostly simultaneous fractional crystallization of the comprising minerals e.g. titanomagnetite, ilmenite and magnesio-hercynite. The temperature and fO2 conditions of re-equilibration are calculated using the compositions of ilmenite and pre-exsolved titanomagnetite pairs. Extrapolation of the data along ulvospinel isopleths reveals the probable original magmatic conditions e.g. temperature ~ 900 °C and fO2 ~ ΔFMQ + 2. The ore forming melt calculated by ‘equilibrium distribution method’ shows no crustal contamination and has a trace elemental pattern similar to typical enriched basaltic melts e.g. ferropicrites, alkali basalts, OIB and EMORB. High Ti and Zr contents of the melt suggest a possible within plate tectonic setting and enrichment in HFSEs and LREEs suggest that the parent melt could be generated from an enriched mantle source by low degree partial melting of garnet-peridotite layer of the upper mantle. The ‘quantitative fractional crystallization modelling’ indicates that early crystallization of olivine, pyroxenes, plagioclase and ilmenite from an enriched basaltic melt similar to EMORB (most fit melt) led to a condition of high oxygen fugacity and iron enrichment in the residual melt. The residual Fe-Ti rich melt moved to low pressure zones within the gabbronorite sill during late stage of D2 deformation, and later crystallized in the form of present ore bodies.

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.

Formation of the Weiya magmatic Fe–Ti oxide deposit and its ore-hosting layered gabbro intrusion, Eastern Tianshan (Xinjiang, NW China)

The Weiya is the largest magmatic Fe–Ti oxide deposit in the Chinese Eastern Tianshan orogen, and is divided into an eastern, central and western section by younger granitoid and diabase intrusions. The Weiya eastern section contain Fe-Ti oxide ores and ore-bearing apatite-poor layered gabbro, which display significant difference in mineral assemblage from the layered gabbro in the central section. We presented new data on the geology, mineralogy, petrology, geochemistry, geochronology, and Sr-Nd isotopes of the gabbroic rocks and the Fe-Ti oxide ores from the eastern section. Igneous zircons from the Weiya anorthosite yielded a SIMS U–Pb concordia age of 237.9 ± 0.71 Ma, coeval with the apatite-rich gabbro in the central section. The gabbroic rocks and Fe-Ti oxide ores in the eastern section and the central section have parallel chondrite-normalized REE patterns and N-MORB-normalized multi-element patterns, together with highly-similar Sr-Nd isotope features, suggesting that the two are comagmatic. Olivine Fo value (62.0–66.7), clinopyroxene Mg# number (68.1–76.2) and plagioclase An contents (39.9–55.4) suggest that the Weiya parental magma was highly evolved after extensive fractional crystallization in the deeper magma chamber, and the residual magma became increasingly oxidized and metals- and volatiles-rich. During the magma emplacement, plagioclase accumulated extensively in the magma chamber roof and further enriched Fe–Ti in the residual melts, leading to Fe–Ti oxide mineralization.

Genetic classification, distribution and ore genesis of major PGE, Co and Cr deposits in China: A critical review

Major platinum-group element (PGE), cobalt (Co) and chromium (Cr) deposits in China are commonly associated with mafic-ultramafic rocks regardless magmatic or hydrothermal origins. Nearly all PGE and half of Co resources in China are from magmatic Ni-Cu-(PGE) sulfide deposits hosted in mafic-ultramafic intrusions. Major resources of Cr are from podiform chromite deposits associated with the mantle sequences of ophiolites, including the Luobusha chromite deposit in Tibet and the Sartohay chromite deposit in Xinjiang. However, there is a lack of large PGE and chromite deposits related to layered mafic-ultramafic intrusions. Sedimentary rock-hosted stratiform Cu deposits and Ni-Co laterites are two dominant types of Co-bearing deposits among terrestrial Co resources and are sporadically distributed in China, although these are insignificant. Platinum-group elements from three Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions that formed within-plate settings account for 74% of the total PGE reserves of China. Among these, the Jinbaoshan and Yangliuping intrusions are parts of the Emeishan large igneous province (LIP) in SW China, and the Jinchuan intrusion emplaced in a rifting margin of the southern North China Craton. The Jinbaoshan intrusion hosts the only PGE-dominated deposit in China, but has not yet been mined due to the difficulty for access. In the Jinchuan and Yangliuping Ni-Cu deposits, PGEs are by-products. The Jinchuan intrusion is by far the largest PGE producer in China. Cobalt resources are from deposits associated with mafic-ultramafic rocks in China, including Ni-Cu sulfide deposits, Ni-Co laterites, volcanogenic massive sulfide (VMS) deposits and magmatic Fe-Ti oxide deposits, which make up 41% of total Co reserves of China. Major Ni-Cu sulfide deposits in both within-plate and convergent margin settings contain economic Co resources, such as the Jinchuan intrusion and those in the Emeishan LIP, and the Xiarihamu intrusion in the East Kunlun orogenic belt, the Jianchaling intrusion in a Neoproterozoic subduction zone in the northern margin of the Yangtze block and those in the central Asian orogenic belt. Ni-Co laterites that contain economic Co resource have been only discovered locally in Hannan, Yunnan and Taiwan. The Derni Cu-Co deposit in the A’nyemaqen suture zone of the East Kunlun orogenic belt is a special type of VMS deposits closely associated with ophiolite suites, which is also very rare worldwide. Magmatic Fe-Ti oxide deposits in the Emeishan LIP and hydrothermal iron oxide deposits in the East Tianshan orogenic belt have likely potential Co resources. Podiform chromite deposits in China occur in ophiolites, such as the Sartohay, Hegenshan and Suolunshan ophiolites in the central Asian orogenic belt, the Dadao Erji and Yushi ophiolites in the Qilian-Qinling orogenic belt, the Dongqiao ophiolite in the Bangong-Nujiang suture zone and Luobusha ophiolite in the Yarlung-Zangbo suture zone. Understanding the mechanisms of PGE enrichment in major Ni-Cu-(PGE) sulfide deposits such as the Jinchuan and Jinbaoshan intrusions has been a focus of studies in the past. The dissolution and re-precipitation processes that may lead to the enrichment of PGE and Co during hydrothermal overprints on magmatic Ni-Cu sulfide deposits have gained popularity. The origin of podiform chromite deposits is generally thought to be triggered by melt-mantle interaction and melt mixing. But it appears that such a traditional thought is challenged by the discoveries of various high-pressure and hydrous minerals that are trapped in chromite. Given PGE, Co and Cr are all strategic and critical metals to China, it is very important to conduct new exploration projects near active mines, such as those in the Emeishan LIP and the Jinchuan intrusion. However, additional experimental and mineralogical studies on the enrichment processes of PGE, Co and Cr are desired to make breakthroughs in order to better understand the behaviors of PGE, Co and Cr in magmatic-hydrothermal systems. Main issues that are worthy to be closely examined in the future include (1) micro- to nano-scale occurrence of PGE, (2) enrichment mechanism and occurrence of Co in mafic-ultramafic rocks and related ore deposits, and (3) mobilization and enrichment processes of Cr in the formation of podiform chromite deposits.

Apatite-hosted melt inclusions from the Panzhihua gabbroic-layered intrusion associated with a giant Fe–Ti oxide deposit in SW China: insights for magma unmixing within a crystal mush

The ∼ 2-km-thick Panzhihua gabbroic-layered intrusion in SW China is unusual because it hosts a giant Fe–Ti oxide deposit in its lower zone. The deposit consists of laterally extensive net-textured and massive Fe–Ti oxide ore layers, the thickest of which is ∼ 60 m. To examine the magmatic processes that resulted in the Fe enrichment of parental high-Ti basaltic magma and the formation of thick, Fe–Ti oxide ore layers, we carried out a detailed study of melt inclusions in apatite from a ∼ 500-m-thick profile of apatite-bearing leucogabbro in the middle zone of the intrusion. The apatite-hosted melt inclusions are light to dark brown in color and appear as polygonal, rounded, oval and negative crystal shapes, which range from ∼ 5 to ∼ 50 µm in width and from ∼ 5 to ∼ 100 µm in length. They have highly variable compositions and show a large and continuous range of SiO2 and FeOt with contrasting end-members; one end-member being Fe-rich and Si-poor (40.2 wt% FeOt and 17.7 wt% SiO2) and the other being Si-rich and Fe-poor (74.0 wt% SiO2 and 1.20 wt% FeOt). This range in composition may be attributed to entrapment of the melt inclusions over a range of temperature and may reflect the presence of µm-scale and immiscible Fe-rich and Si-rich components in different proportions. Simulating results for the motion of Si-rich droplets within a crystal mush indicate that Si-rich droplets would be separated from Fe-rich melt and migrate upward due to density differences in the interstitial liquid when the magma unmixed. Migration of the Si-rich, immiscible liquid component from the interstitial liquid caused the remaining Fe-rich melt in the lower part to react with plagioclase primocrysts (An59–60), as evidenced by fine-grained lamellar intergrowth of An-rich plagioclase (An79–84) + clinopyroxene in the oxide gabbro of the lower zone. Therefore, magma unmixing within a crystal mush, combined with gravitationally driven loss of the Si-rich component, resulted in the formation of Fe-rich, melagabbro and major Fe–Ti oxide ores in the lower part and Si-rich, leucogabbro in the upper part of the intrusion.

Physicochemical Control of the Early Permian Xiangshan Fe-Ti Oxide Deposit in Eastern Tianshan (Xinjiang), NW China

The Xiangshan mafic-ultramafic complex is one of the major Early Permian mafic-ultramafic intrusions in eastern Tianshan (Xinjiang, NW China), and consists of two major intrusive phases. The first intrusive phase is mainly gabbroic rocks hosting ilmenite mineralization, while the second intrusive phase is mainly lherzoilite associated with Ni-Cu sulfide mineralization. The Xiangshan ilmenite orebodies hosted in the Fe-Ti oxide-bearing gabbro occur along the contact between hornblende gabbros and leucogabbros. The hornblende gabbros and Fe-Ti oxide rich gabbros at Xiangshan are newly dated to be Early Permian (280.1 and 279.2 Ma, respectively). Major and trace element compositions of zircons and whole rocks from Xiangshan hornblende gabbro and Fe-Ti oxide gabbro have been measured by in situ excimer laser ablation ICP-MS. Zircon Ce4+/Ce3+ ratios based on lattice-strain model and Ti-in-zircon temperatures of hornblende gabbro and Fe-Ti oxide gabbro of the Xiangshan complex are calculated to evaluate the physicochemical variations during the ilmenite mineralization. Whole-rock geochemistry and zircon trace element geochemistry suggest that Fe-Ti oxide gabbros were formed from a basaltic parent magma which had undergone a transfromation from being H2O-rich to H2O-poor. During the magmatic evolution, primitive, H2O-poor basaltic melts may have been replenished into the system, increasing its solidus temperature and decreasing its oxygen fugacity and H2O contents. This may have supperessed the Ti-rich poikilitic hornblende fractionation and promoted the plagioclase fractionation, which consequently concentrated the ore-forming components in the residual melts and generated the ilmenite mineralization.

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.

Platinum-group element geochemistry of the layered intrusions in the Emeishan large igneous province, SW China: Implications for the principal controls on magmatic sulfide immiscibility

It is widely accepted that the incorporation of external sulfur via crustal contamination is an important trigger for sulfide immiscibility that generates Ni-Cu-(PGE) sulfide mineralization, yet other controlling factors for sulfide immiscibility may also be present. The late Permian Panzhihua, Baima, Hongge, Xinjie and Taihe layered intrusions in the Emeishan Large Igneous Province (ELIP, SW China), are well-endowed with Fe-Ti oxide deposits, whereas their sulfide mineralization is mainly sub-economic. For example, the lower part of the Xinjie intrusion hosts a few thin PGE-rich ore layers, yet other ELIP layered intrusions do not contain any Ni-Cu sulfide mineralization and are PGE-depleted (0.01–1 ppb). Compared with the PGE-undepleted Emeishan high-Ti basalts that are genetically related to the intrusions, the extent of PGE depletion and elevated Cu/Pd ratios (up to 3.2×106) of the Panzhihua, Baima, Taihe and Hongge intrusions suggest PGE-depletion in their parental magmas due to early-stage sulfide removal. Sr-Nd isotopic compositions of the Panzhihua, Baima and Taihe intrusions suggest crustal contamination was insignificant and sulfide saturation produced mainly by crustal sulfur input was unlikely. MELTS modeling shows that extensive fractionation of chromite, olivine and clinopyroxene in deep-seated magma chambers may have induced early-stage sulfide saturation of the primary magmas. The relatively high sulfide contents in the Fe-Ti oxide layers at Panzhihua, Baima, Hongge and Taihe indicate a close relationship between the second-stage sulfide immiscibility and extensive Fe-Ti oxide crystallization. Positive correlations between sulfur and total Fe2O3, V and TiO2 suggest that Fe-Ti oxide (magnetite and ilmenite) crystallization may have triggered the second-stage sulfide saturation via sharply lowering the Fe concentration and oxygen fugacity of the magmas. Moderate degree of crustal contamination for the Xinjie Fe-Ti oxide-barren rocks may have induced sulfide saturation and accumulation at the lower part of the intrusion. Our calculations indicate that the Xinjie PGE-rich rocks have high R-factors (1000–10000), which are ascribed to PGE-upgrading of the sulfides via reaction with new replenishments of PGE-undepleted magmas. A few Panzhihua, Baima and Taihe samples that contain higher PGE concentrations suggest that the early-stage sulfide droplets at depths were entrained in later magma pulses delivered to shallower magma chambers. The very high R-factors determined by mass balance calculation, implies a good potential for discovering more PGE mineralization in the deep-seated intrusions of the magma plumbing system.

Association of Mg-rich Olivine with Magnetite as a Result of Brucite Marble Assimilation by Basaltic Magma in the Emeishan Large Igneous Province, SW China

An unusual feature of the magmatic Fe-Ti oxide deposits associated with layered intrusions in the Permian Emeishan large igneous province (LIP) in SW China is the association of the mineralization with olivine that is significantly more Mg-rich than those that occur elsewhere. A working hypothesis for the production of Mg-rich olivine is that significant assimilation of carbonate occurred during the formation of the Fe-Ti oxide deposits in the Emeishan LIP. This study provides several lines of supporting evidence from a coeval picritic dyke in the footwall of the Panzhihua layered intrusion at Zhujiabaobao. Country rocks to the Zhujiabaobao picritic dyke are brucite marbles. Olivine phenocrysts in the dyke have Fo contents varying from 79 to 91 mol %. The most Mg-rich olivine phenocrysts (Fo89-91) are present in the margins of the dyke and contain undissolved calcite. Olivine phenocrysts in the marginal sample show reversed zoning in Fo content and contain similar to 20% lower Ni than those with similar Fo contents in the coeval picrites emplaced in the nearby area. Olivine-hosted oxide inclusions in this sample are exclusively Cr-magnetite (calculated atomic Fe3+/Cr3+ > 1) instead of chromite or Cr-spinel (calculated atomic Fe3+/Cr3+ (Nd) values (1 center dot 4-2) but contrasting Sr isotope compositions. The sample with the most Mg-rich olivine (Fo89-90) has the highest initial Sr-87/Sr-86 ratio (0 center dot 7054), whereas samples with more Fe-rich olivine (Fo78-83) have lower initial Sr-87/Sr-86 ratios (0 center dot 7046-0 center dot 7049). The results of mixing calculations indicate that up to similar to 25 wt % assimilation of brucite marble by basaltic magma with a composition similar to that of the average of the coeval high-Ti basalts can readily explain the observed mineralogical and isotopic variations within the dyke. The results from the dyke show that carbonate assimilation by basaltic magma is an efficient way to produce the association of magnetite with olivine that is anomalously rich in magnesium.