Small Mafic-ultramafic Intrusions Research Articles

Mg–Sr–Nd isotopic constraints on the genesis of the giant Jinchuan Ni–Cu–(PGE) sulfide deposit, NW China

Magmatic sulfide deposits are principal resources of nickel and platinum-group elements (PGE) in the world. These deposits form as the result of the concentration of immiscible sulfide-liquid droplets segregated from mafic or ultramafic magma. Sulfide saturation in the magmas is commonly linked to contamination by the continental crust. The Jinchuan Ni–Cu–(PGE) deposit is the largest single magmatic sulfide deposit in the world. It is hosted by a small mafic–ultramafic intrusion in the North China Craton. The Jinchuan mafic–ultramafic intrusion intruded Paleoproterozoic marbles, gneisses, and granitic migmatites. This paper reports the magnesium, strontium and neodymium isotopic compositions of the intrusion and the country rocks. Olivine, pyroxene and whole rocks of the lherzolites from the Jinchuan intrusion have δ26Mg values ranging from −0.40‰ to −0.26‰, with a weighted mean value of −0.31 ± 0.06‰ (2SD), which is slightly lighter than expected in a mantle-derived magma. The marble country rocks have relatively light δ26Mg values varying from −2.00‰ to −1.17‰, with a weighted mean value of −1.53 ± 0.02‰ (2SD). The variations are attributed to the interaction between basaltic magma and marble country rocks as the principal mechanism which generated the low Mg isotopic signatures in the Jinchuan deposit. The (87Sr/86Sr)i and εNd values of the lherzolites vary from 0.706615 to 0.714612 and from −8.29 to −6.13, respectively. The marble country rocks have relatively high (87Sr/86Sr)i ratios (0.713662 to 0.740069) and low εNd values (−25.43 to −12.41). The negative Nb anomalies in all samples from the intrusion indicate that the parental magma underwent crustal contamination. Mg–Sr–Nd isotopic mixing calculations indicate that the Jinchuan intrusion underwent 10–20% bulk contamination involving the lower continental crust, followed by <10% bulk contamination by marbles. Our petrological and geochemical investigation of the Jinchuan intrusion provides evidence that a combination of the two processes led to the formation of the ore deposit. The assimilation of lower crustal rocks reduced the sulfur solubility; the assimilation of marble country rocks made the magma more oxidized and hence decreased the sulfur solubility further. The results from this study show that Mg isotopes are useful in the study of carbonate assimilation by mafic magma, and marble assimilation by basaltic magma is an important mechanism to produce sulfide saturation in the genesis of Ni–Cu–PGE sulfide deposits.

Temporal variations in the mantle source beneath the Eastern Tianshan nickel belt and implications for Ni–Cu mineralization potential

Many small mafic–ultramafic intrusions are found in the Eastern Tianshan Ni belt along the southern margin of the Central Asian Orogenic Belt (CAOB). The Ni–Cu mineralized Hulu intrusion is located in the eastern part of the Jueluotage area of the Eastern Tianshan Ni belt. This mafic–ultramafic intrusion comprises a shallow layered sequence and deeper dike-like unit. Precise zircon U–Pb dating yielded ages of 381.0 ± 1.3 and 377.0 ± 3.0 Ma for sulfide-bearing samples from the layered unit and 388.6 ± 2.7 Ma for a mineralized gabbro from the dike-like unit. 176Hf/177Hf values of zircons from the layered unit range from 0.282846 to 0.283165 and correspond to εHf(t) values of +10.6 to +20.4. δ18O values for these zircons range from +4.8‰ to +5.5‰. Similarly, zircons from the sulfide-bearing gabbro of the dike-like unit have εHf(t) and δ18O values from +13.0 to +18.2 and +5.0‰ to +5.6‰, respectively. Normalized SiO2, Al2O3, TiO2, and Na2O + K2O contents increase with decreasing MgO content, whereas the FeOtotal content is positively correlated with MgO, which indicates that the different lithologies resulted from the fractional crystallization of a common parental magma. Furthermore, the mafic–ultramafic intrusions and their calculated parental magmas in the Jueluotage area have similar rare earth element (REE) patterns with slight enrichment of the light REE relative to heavy REE. All of the rocks and estimated parental magmas exhibit depletions in high-field-strength elements (HFSE; e.g., Nb, Ta, and Zr) and enrichments in large-ion lithophile elements (LILE; e.g., U). The pronounced light REE and LILE enrichments and HFSE depletions of the mafic–ultramafic intrusions and calculated parental magmas are indicative of a subduction-modified mantle source. Clinopyroxenes in the Hulu intrusion have variable Al2O3 (4.39–7.32 wt%) and low TiO2 (0.33–0.67 wt%) contents, which are comparable to typical Alaskan-type complexes that were emplaced in subduction environments. In a TiO2 versus Alz (AlIV × 100/2) diagram, data for the Devonian mafic–ultramafic intrusions in the Jueluotage area fall within the fields of Alaskan-type complexes, whereas data for most of the Permian intrusions fall outside of these fields. Systematic in situ zircon O and Hf isotope analyses from the Devonian mafic–ultramafic intrusions in the Jueluotage area exhibit higher δ18O and lower εHf(t) values than those of the Permian intrusions, which may be explained by a change from a Devonian fluid- to Permian fluid- and melt-modified mantle source. The mafic–ultramafic intrusions that were emplaced in both subduction and post-collisional extensional environments in the Eastern Tianshan Ni belt were favorable hosts to magmatic Ni–Cu deposits, despite their different mantle sources.

BLADE-SHAPED DIKES AND NICKEL SULFIDE DEPOSITS: A MODEL FOR THE EMPLACEMENT OF ORE-BEARING SMALL INTRUSIONS

Most of the world's major deposits of nickel and copper were formed as accumulations of magmatic sulfide liquid within small mafic-ultramafic intrusions. Ore-hosting intrusions exhibit a variety of forms but typically show greater horizontal than vertical extents, occurring as tube-shaped chonoliths, narrow elongate sills, boatshaped bodies, or sword blade-shaped dikes with originally horizontal principal axes. Sulfide accumulation at the downward termination of blade-shaped dikes is noted in a number of deposits worldwide. Based on evidence from continental dike swarms, Icelandic fissure eruptions, and active shield volcanoes, we suggest that these blade-shaped bodies formed by magma migration within vertical fractures that propagated laterally rather than vertically. Some examples, notably the bladed dikes of the South Raglan trend, have contact relationships indicating processes of active erosion, assimilation, and replacement of country rock. Where such dikes are injected into mixed volcanic-sedimentary sequences, thermal modeling of interaction with nonrefractory country rock predicts repeated formation and collapse of transient chilled margins against narrow zones of partially molten wall rock. Where the wall rock is sulfide-rich sediment, this generates a slurry of sulfide liquid, country-rock xenoliths, and chilled margin fragments that flows down the wall to accumulate at the bottom edge of the dike. This type of mixture is commonly seen as sulfide-matrix ore breccias in intrusion-hosted deposits. Widening of the conduit along zones of easily eroded country rock may result in a transition from a dike-like to a tubular chonolith geometry. Multiple magma pulses within the same magma conduit may give rise to complex superimpositions of ore zones, further complicated by formation of sulfide-silicate melting-infiltration fronts. Hence we argue that the bladed-dike geometry is an end-member type that commonly serves as a precursor form to a range of eventual geometric forms; recognition of this basic geometry provides general insights into the origins of other important deposits.

Precious metal mineralisation in the Sotkavaara Intrusion, northern Finland: Peak Pt, Pd, Au and Cu offsets in a small intrusion with poorly-developed magmatic layering

The Sotkavaara Intrusion is a small (2.5×1.5km surface expression) mafic-ultramafic intrusion located in northern Finland, 25km east-southeast of Rovaniemi. The intrusion was drilled by the Geological Survey of Finland between 2009 and 2012, when low-S, low-grade precious metal mineralisation (<1.1ppm Pt+Pd+Au) was discovered. Emplaced into the 1.98Ga eastern Peräpohja Schist Belt, Sotkavaara occurs a few tens of kilometres north of the 2.44Ga the Penikat, Portimo and Koillismaa intrusions, which together host Europe’s most significant platinum-group element (PGE) mineralisation. The intrusion comprises a volumetrically subordinate Gabbro Unit and volumetrically dominant Pyroxenite Unit, within which layering is poorly-developed. The Pyroxenite Unit is composed predominantly of clinopyroxenite and contains a small number of laterally discontinuous wehrlite, olivine clinopyroxenite and low-Cr clinopyroxenite (<0.1wt% Cr2O3) layers. Precious metal mineralisation is hosted by low-Cr clinopyroxenite layers and shows systematic Pt, Pd, Au and Cu offsets similar to those in the Munni Munni, Rincón del Tigre, Skaergaard and Great Dyke intrusions. Relative to these global examples, the Sotkavaara Intrusion represents an atypical occurrence, exhibiting poorly-developed modal layering in a small mafic-ultramafic intrusion, alongside moderately heavy δ 34S values (+1.3 to +9.6‰). Despite this, mineralisation can be broadly attributed to similar ore-forming processes, whereby in-situ fractional crystallisation is ultimately responsible for generating small volumes of sulphide melt. Although mineralisation is sub-economic, this occurrence indicates that northern Finland may be prospective for magmatic sulphide deposits in Svecofennian-age mafic-ultramafic intrusions. Globally, Sotkavaara highlights that well-developed modal layering and large magma chambers are not necessarily requirements for forming this type of mineralisation.

The role of crustal contamination in the formation of Ni–Cu sulfide deposits in Eastern Tianshan, Xinjiang, Northwest China: Evidence from trace element geochemistry, Re–Os, Sr–Nd, zircon Hf–O, and sulfur isotopes

Tulaergen, Xiangshan, Huangshan, Tianyu, and Baishiquan magmatic Ni–Cu sulfide deposits, which are all located in the eastern part of the Central Asian Orogenic Belt, and associated with small mafic–ultramafic intrusions with high-grade Cu and Ni orebodies have similar ages of formation. Their magma sources are MORB-like and OIB-like depleted mantle. Modeling calculations of Sr–Nd and zircon Hf isotopic data show that about 10–15% of oceanic slab components are added into the source of Baishiquan and Tianyu intrusions, but only less than 5% are in the three other intrusions. The higher degree of subduction metasomatism in the Baishiquan and Tianyu magma sources is likely the result of the Paleozoic multiple-stage subduction. Moreover, the relative enrichment of LILE, depletion of HFSE, and lower Ce/Pb ratios indicate that these intrusions experienced crustal contaminations. The effects of crustal contamination are also identified in the magmatic sulfide deposits by the higher zircon δ18O, higher sulfide γOs, and δ34S values observed. We propose a two-stage crustal contamination model of the Tulaergen, Xiangshan, Tianyu, and Baishiquan intrusions. However, the Huangshan intrusion, which has the highest degree of crustal contamination, likely experienced only single-stage upper crustal contamination (∼14.2%). The addition of crustal S appears to be directly related to triggering S saturation in these deposits. According to a simple S isotopic modeling calculation, 11%, 2.9%, 1.2% and 2.1% of the crustal sulfur addition into the parental magma would be required to form the Tianyu, Baishiquan, Xiangshan, and Tulaergen deposits, respectively.

Magmatic Ni-Cu-(PGE) deposits in magma plumbing systems: Features, formation and exploration

The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are: (1) a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposits; (2) fractional crystallization and crustal contamination, particularly the input of sulfur from crustal rocks, resulting in sulfide immiscibility and segregation; and (3) the timing of sulfide concentration in the intrusion. The super-large magmatic Ni-Cu sulfide deposits around the world have been found in small mafic-ultramafic intrusions, except for the Sudbury deposit. Studies in the past decade indicated that the intrusions hosting large and super-large magmatic sulfide deposits occur in magma conduits, such as those in China, including Jinchuan (Gansu), Yangliuping (Sichuan), Kalatongke (Xinjiang), and Hongqiling (Jilin). Magma conduits as open magma systems provide a perfect environment for extensive concentration of immiscible sulfide melts, which have been found to occur along deep regional faults. The origin of many mantle-derived magmas is closely associated with mantle plumes, intracontinental rifts, or post-collisional extension. Although it has been confirmed that sulfide immiscibility results from crustal contamination, grades of sulfide ores are also related to the nature of the parental magmas, the ratio between silicate magma and immiscible sulfide melt, the reaction between the sulfide melts and newly injected silicate magmas, and fractionation of the sulfide melt. The field relationships of the ore-bearing intrusion and the sulfide ore body are controlled by the geological features of the wall rocks. In this paper, we attempt to demonstrate the general characteristics, formation mechanism, tectonic settings, and indicators of magmatic sulfide deposits occurring in magmatic conduits which would provide guidelines for further exploration.

The Permian Huangshanxi Cu–Ni deposit in western China: intrusive–extrusive association, ore genesis, and exploration implications

The Permian Huangshanxi Cu–Ni deposit is the second largest magmatic sulfide deposit discovered to date in a major Ni–Cu province related to protracted basaltic magmatism in eastern Xinjiang, China. It is hosted by a small mafic–ultramafic intrusion comprised predominantly of lherzolites, olivine websterites, gabbronorites, and gabbros. The Huangshanxi intrusion is coeval with Permian basalts of tholeiitic and alkaline affinities in the Tuha and Tarim basins, respectively. To evaluate a possible genetic relationship between the Huangshanxi intrusion and a specific type of coeval basalt in the region, as well as ore genesis in the intrusion, we have carried out an integrated mineralogical, petrological, and geochemical study. Our data reveal that the Huangshanxi intrusive rocks are characterized by relatively flat chondrite-normalized REE patterns, depletion in Nb and Ta, and elevated eNd values varying between 6 and 10. These features are similar to those of coeval tholeiitic basalts in the nearby Tuha basin, but are significantly different from those of coeval alkaline basalts in the relatively remote Tarim basin. The geochemical similarities and differences suggest that the Huangshanxi intrusion is genetically related to the tholeiitic basalts in the Tuha basin, not to the alkaline basalts in the Tarim basin, as suggested previously by some researchers. This implies that regional exploration for the Huangshanxi-type Cu–Ni deposits should be centered in the Tuha basin instead of the Tarim basin. More specifically, the uplifted areas around the Tuha basin where similar intrusions may have been brought close to the surface should be carefully examined for mineralization potential. Intrusive relations and mass balance constraints from incompatible trace elements and sulfide abundances suggest that the Huangshanxi intrusion represents a dynamic magma conduit through which multiple pulses of magma ascended to higher levels or to the surface. Numerical simulation of magma evolution and mixing calculations using Sr–Nd isotopes indicate that selective assimilation of S-bearing crustal materials is important for sulfide saturation during the early stages of magma evolution when lherzolites formed. Fractional crystallization may have also played a role in the attainment of sulfide saturation during the later stages of magma evolution when olivine websterites and gabbronorites formed. In both cases, immiscible sulfide droplets were retained in the conduit to form disseminated sulfide lenses while the fractionated silicate liquids and buoyant phases such as plagioclase continued to ascend. Extremely low PGE tenors in the sulfide ores of the Huangshanxi deposit suggest that the parental magma was highly depleted in chalcophile elements possibly due to previous sulfide segregation at depth.

Devonian to Permian plate tectonic cycle of the Paleo-Tethys Orogen in southwest China (I): Geochemistry of ophiolites, arc/back-arc assemblages and within-plate igneous rocks

The Paleo-Tethys Orogen in southwest China is an amalgamation of continental terranes (Sibumasu, Simao and Yangtze), which are bounded by ophiolite belts (Ailaoshan, Jinshajiang and Changning–Menglian) that represent former ocean basins. This study concentrates on ophiolites, arc/back-arc assemblages, and within-plate igneous rocks that occur in this complex orogen. Mainly based on geochemical fingerprinting of basalts, the Paleo-Tethys ophiolites are here classified as MORB and SSZ types. The Ailaoshan ophiolite (NMORB-type; ca. 387–374 Ma) is associated with a non-volcanic segment of the rifted western Yangtze margin. The Jinshajiang ophiolite (EMORB-type; 346–341 Ma), which has ophiolite structure but some samples bear crustal contamination signatures, is associated with a volcanic segment of the rifted Yangtze western margin. These MORB-type ophiolites are interpreted to have formed in the continent-ocean transition zones. The Changning–Menglian ophiolite, which marks the main Paleo-Tethys suture, that is, the boundary between the Gondwana-derived Sibumasu terrane and the Yangtze-derived Simao terrane, has traditionally been thought to have a mid-ocean ridge (MOR) origin. New trace element data of basalts, however, indicate that this ophiolite (ca. 270–264 Ma) was formed at a supra-subduction zone (SSZ). Arc and back-arc assemblages are represented by the Gicha (ca. 311–277 Ma) and Banpo (ca. 288–284 Ma) zoned mafic-ultramafic complexes and the Yaxianqiao arc volcanic rocks (ca. 268–264 Ma). Geochemical data suggest that the Gicha complex originated in a back-arc rift. The Banpo complex makes a plutonic arc that contains low-Ti gabbro and tonalite with volcanic arc granite (VAG) affinity. Within-plate igneous rocks are recognized as xenoliths (amphibolites; ca. 443–401 Ma) in the Jinshajinag ophiolite mélange and the Dalongkai small differentiated mafic-ultramafic intrusion (ca. 247–244 Ma) that intruded the Yaxianqiao Arc. The amphibolite xenoliths are similar to low-Ti continental flood basalts (CFB) in composition. Rocks from the small mafic-ultramafic intrusion have superimposed subduction and within-plate geochemical signatures. These ophiolites, arc/back-arc assemblages and within-plate igneous rocks, are summarized as the magmatic records for the Plaeo-Tethys evolution in the context of a plate tectonic cycle.

Mineralogical, petrological, and geochemical studies of the Limahe mafic–ultramatic intrusion and associated Ni–Cu sulfide ores, SW China

The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.

Unusual PGE distribution in the mafic-ultramafic rocks of the Early Paleoproterozoic (2.5–2.35 Ga) drusite (coronite) complex of the Belomorian region, northern Karelia, Russia

The PGE pattern and PGM was studied in the rocks of numerous small mafic-ultramafic intrusions of the Early Paleoproterozoic (2.46–2.35 Ga) drusite complex of the Belomorian mobile belt, eastern Baltic Shield, Russia. The chondrite-normalized PGE pattern in the studied rocks (gabbronorites, pyroxenites, and plagioclase lherzolites) is similar to that of the primitive mantle, regardless of the composition of these rocks. It was shown for the first time that different rock types of the drusite complex contain minerals of all six PGE, which makes these rocks principally different from the coeval large layered mafic-ultramafic intrusions with Pd-Pt mineralization at the adjacent Kola and Karelian cratons. This is presumably related to the generation conditions of the parental magmas of the siliceous high-magnesian series (SHMS) and to the practically complete absence of differentiation during the emplacement of the intrusions. Owing to this, the drusite intrusions retained the primary PGE distribution, which is presumably typical of the parental melts of SHMS and was only partially modified by allochemical metamorphism.

Genesis of the Permian Baimazhai magmatic Ni–Cu–(PGE) sulfide deposit, Yunnan, SW China

The ~260 Ma-old Baimazhai Ni–Cu–(PGE) sulfide deposit in the Jinping region, Yunnan, SW China, is hosted in a small mafic–ultramafic intrusion, which intruded Ordovician sandstone and slate. The intrusion is concentric with lens shape, about 530 m long, 190 m wide and 24 to 64 m thick, trends 296°, and dips 22°NE. The massive sulfide ore body forms the core of the intrusion and is surrounded by variably mineralized orthopyroxenite, websterite and barren gabbro. The proportion of gabbro, websterite, orthopyroxenite and massive ore is approximately 30, 30, 20 and 20 vol.%, respectively. Magmatic pyrrhotite, pentlandite and chalcopyrite make up more than 90% of the massive ores. The massive ores contain high Ni (1.6 to 4.2 wt%) and Cu (0.4 to 6.5 wt%) and low ∑PGE contents (85 to 524 ppb). They have Pd/Ir ratios ranging from 6.7 to 530, Pd/Pt ratios from 0.7 to 2.6 and Cu/(Pd×1,000) ratios from 31 to 400, which are comparable with those of the silicate rocks [Pd/Ir = 4 to 183, Pd/Pt = 0.7 to 3.5, and Cu/(Pd×1,000) = 100 to 400]. Similar Pd/Pt and Cu/Pd ratios of the silicate rocks and massive ores throughout the intrusion indicate a single sulfide segregation event. Excess sulfide melt segregation resulted from intensive crustal contamination that formed Si-rich and Mg-rich basaltic magmas in a deep-seated staging chamber before magma emplacement. The immiscible sulfide melts and the silicate melts were eventually evacuated from the staging magma chamber by compressive forces. Flow differentiation under high velocity concentrated the sulfide melts toward the middle of the magma flow, and consequently, formed a massive sulfide ore body in the central part of the intrusion. Low concentrations of PGEs and general absence of platinum-group minerals in the massive ores may have resulted from a relatively large mass fraction of the sulfide melts (e.g. R-factor = ~70) in Baimazhai compared with other intrusions elsewhere, such as Noril’sk-Talnakh with a R-factor of >10,000.

MAIS imaging spectrometer data analysis for Ni-Cu prospecting in ultramafic rocks of the Jinchuan group, China

The Jinchuan intrusion, situated in the Gansu province of China some 30 km NE of Yongcang city is an ultramafic dyke-like body emplaced in the Longshoushan uplifted terrain on the southwest margin of the Sino-Korea platform. The intrusion is 6 km long, 35 m wide and hosts a major Ni-Cu sulfide deposit. The main stratigraphic units include the highly metamorphosed Lower Proterozoic Longshoushan group and the less extensively metamorphosed Dongzigou and Hanmushan groups of Middle and Upper Proterozoic age. The Longshoushan group consists of serpentine marble, schist, gneiss and plagioclase amphibolite. The Dongzigou group comprises schists and granitic rocks. The Hanmushan group basically is represented by a large variety of volcanics. Small mafic-ultramafic intrusions are located along faults in the Jinchuan terrain. These ultramafic rock bodies show a concentric zoning with a core of dunites and olivine pyroxenites forming the margins of the bodies. Hydrothermal alteration (mainly serpentinization) has affected the rocks of the ultramafic bodies to a variable extent; the dunites are extensively altered whereas the pyroxene rich units are relatively fresh. Field spectroscopy is used to spectrally characterize the major rock units. Imaging spectrometer data was flown during the end of July until beginning of August of 1993 with a Chinese imaging spectrometer instrument called MAIS: the Modular Airborne Imaging Spectrometer. Feature characterization permits lithologic mapping from MAIS data. This aids in mineral potential mapping in the Jinchuan region and permits the identification of areas of possible Ni-Cu deposits.