The chemical composition of a barren biotite granite, a two-mica granite, and a rare metal-bearing pegmatite (the No. 3 vein in Keketuohai, Altay Mountains, northwest China), along with mineral separates of apatite and mica, were analyzed and compared in the present work. Bulk chemistries of biotite granite, two-mica granite, and pegmatite rim are consistent with fractional crystallization trend from granites toward pegmatite. Changes in pegmatite composition can be explained mainly by fractional crystallization of biotite. Rb–Sr isochrons yield 248.8±7.5 Ma for the biotite granite, 247.8±6.3 Ma for the two-mica granite, and 218.4±5.8 Ma for the pegmatite rim. Similar geochemical characteristics, including initial εNd (T) values (ranging from -0.76 to -3.04) for apatites, similar initial 3Nd (T) values for whole-rock samples of studied granites and pegmatite (ranged from-1.40 to-3.21) and for biotites from granites (ranged from-2.75 to-3.15) suggest that these rocks were derived from a common magma source. Old continental crust may have played a significant role in magma generation. Based on these data, we interpret the evolution of the Keketuohai granite–pegmatite by magma differentiation from a common source. Biotite granite was the first to crystallize, followed by two-mica granites. The residual melt was probably stored in a granitic batholith. The pegmatite veins were injected ～30 M. y. later during another episodic tectono-magmatic event in the Altay Mountains. © 2005 Elsevier Ltd. All rights reserved.

Clinopyroxene phenocrysts in the Kokchetav trachybasalts are variable in composition and textures. Two distinctive cores are recognized: diopside cores and green salite cores. The diopside cores with Mg# of 80–90 are mantled by colorless salite rims with Mg# of 70–80. The green salite cores have especially low Mg# (<70) but high Al and Ti contents. A Mg-rich band (Mg# = 82–90) usually occurs between a green salite core and its rim, and/or between a colorless salite mantle and its rim. Dissolution surfaces are observed on all textural variants. Two magma chambers are needed to explain the observed clinopyroxene phenocrysts. A deep chamber at about 120 km in the upper mantle in which diopside cores crystallized, and a shallow chamber at depths of less than 40 km in which diopside cores were resorbed and overgrown by salite rims or mantles. Magma mixing in the shallow chamber is responsible for the formation of dissolution surfaces between the diopside bands and the colorless salite mantles. The dissolution surfaces on the diopside cores formed in the shallow chamber as a result of pressure decrease. This magma evolution scenario is complicated by the occurrence of the crustal-origin green salite cores in diopsides. These green cores likely represent the relics of continental materials, which were captured in the deep chamber and partially re-melted. Our observations indicate that subducted continental materials were returned to the Earth’s surface as a result of magmatism. This study therefore provides direct evidence of a link between subducted continental materials (slab) and magmatism in this orogenic belt. © 2003 Elsevier Ltd. All rights reserved.

The dolomite-dissociation textures documented here in rocks from the Kokchetav ultrahigh-pressure massif suggest that the experimentally expected dolomite dissociation happened in the subducted slabs represented by these rocks. Two reactions, magnesite=C + MgO + O2, and majoritic garnet + MgO + H2O = garnet + clinochlore, recorded in carbonate inclusions and the host majoritic garnet are responsible for generation of graphite and clinochlore during the exhumation. The dolomite dissociation indicates that carbonate materials were subducted to depths of .250 km below Earth’s surface. Such deep subduction evidently brings abundant carbon and carbonate into deep Earth.

The Wangfeng–Tianger–Saridala ore district consists of over 20 orebodies with total proven gold reserves exceeding 15 tonnes. The district is located on the EW-striking Tianger (Bingdaban) shear zone in west Tianshan Mountains, northwest China. The lensoid orebodies are distributed along the shear zone in a region about 25 km in length and 1 km in width. Enhanced fluid flow and fracturing controlled location and orientation of mineralized zones during deformation along narrow shear bands oriented oblique to the overall shear zone margins. Fabrics in fractures and strain shadow overgrowths generally plunge steeply, parallel to the lineation in the surrounding cataclasite matrix consisting of new grains of quartz and minor amounts of micas. Native gold occurs inmylonitized granites ormylonitized sulfide–mica–quartz veins.Gold grade is closely relatedwith the occurrence of sulfide–quartz veins. Pyrite and pyrrhotite in gold-bearing sulfide–quartz veins contain inclusions of native gold. Chondrite-normalized rare earth element (REE) distribution patterns for pyrite from the orebodies show light REE enrichments and negative Eu anomalies. Relationships between gold contents and Th/U, Zr/Hf and (La/Yb)N values for pyrites imply that gold-rich pyrites are different from goldpoor pyrites, thus indicate that the pyrites in the orebodies have a different origin compared with those in wall rocks. A Rb–Sr isochron for the mylonitized Au-bearing quartz veins indicates an age of 224±14 Ma with an initial 87Sr/86Sr ratio of 0.7294±0.0089 (MSWD=1.1). This age is conformed by 40Ar/39Ar dating on muscovites (220.9 to 222.5Ma), which is interpreted as the age of ore-formation in the Tianger deposit. High initial 87Sr/86Sr ratios (0.7294), high δ34S values (+11.2 to +16.5‰), low δ18OH2O values (1.67 to 3.07‰) and low δD values (−84 to −104‰) indicate that the ore-forming fluid was unrelated to any magmatic process. © 2006 Elsevier B.V. All rights reserved.

Kokchetav ‘lamproite’ occurs in the east end of Kokchetav massif and consists of phenocryst (mainly clinopyroxene) and matrix (mainly feldspar). The compositions of clinopyroxene, magnetite and biotite phenocryst were determined using wavelength dispersive spectrometry on a JEOL Super-probe 8900 electron microprobe for the purpose of revealing the process of magma evolution. Analyses revealed a core-rim variation, which is consistent with three stages of magmatic evolution: Mg-rich clinopyroxene cores (diopside) and biotite cores (phlogopite) crystallized in a deep magma chamber (stage I); Fe-rich clinopyroxene rim (salite) and biotite rim crystallized at low pressure in a shallow magma chamber (stage II); Magnetite phenocryst core also crystallized in a shallow magma chamber, and coexists with Fe-rich clinopyroxene rim and biotite rim. The magnetite rims probably formed during magma eruption at the same time when groundmass crystallized (stage III).The calculated temperatures for ilmenite-magnetite pair range from 679 to 887ºC, log fO2 values range from 311.1 to 314.9 log units. These values represent the latest conditions of magma as ilmenite exsolution in magnetite probably occurred during magma eruption from the shallow chamber to surface. © 2002 Elsevier Science B. V. All rights reserved.