Cenozoic tectonic evolution of the central Wassuk Range,western Nevada,USA

The central Wassuk Range is ideally located to investigate the interplay of Basin and Range extension and Walker Lane dextral deformation along the western Nevada margin of the Basin and Range province. To elucidate the Cenozoic evolution of the range, the author conducted geologic mapping, structural data collection and analysis, geochemical analysis of igneous lithologies, and geochronology. This research delineates a three-stage deformational history for the range. A pulse of ENE–WSW-directed extension at high strain rates (～8.7 mm/yr) was initiated immediately after the eruption of ～15 Ma andesite flows; strain was accommodated by high-angle, closely spaced (1–2 km), east-dipping normal faults which rotated and remained active to low angles as extension continued. A post-12 Ma period of extension at low strain rates produced a second generation of normal faults and two prominent dextral strike–slip faults which strike NW, subparallel to the dextral faults of the Walker Lane at this latitude. A new pulse of ongoing extension began at ～4 Ma and has been accomodated primarily by the east-dipping range-bounding normal fault system. The increase in the rate of fault displacement has resulted in impressive topographic relief on the east flank of the range, and kinematic indicators support a shift in extension direction from ENE–WSW during the highest rates of Miocene extension to WNW–ESE today. The total extension accommodated across the central Wassuk Range since the middle Miocene is >200%, with only a brief period of dextral fault activity during the late Miocene. Data presented here suggest a local geologic evolution intimately connected to regional tectonics, from intra-arc extension in the middle Miocene, to late Miocene dextral deformation associated with the northward growth of the San Andreas Fault, to a Pliocene pulse of extension and magmatism likely influenced by both the northward passage of the Mendocino triple junction and possible delamination of the southern Sierra Nevada crustal root.     

A Periglacial Palaeoenvionment in the Upper Carboniferous–Lower Permian Tobra Formation of the Salt Range, Pakistan

The Upper Carboniferous—Lower Permian(Upper Pennsylvanian-Asselian) Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan.The formation exhibits an alluvial plain(alluvial fan-piedmont alluvial plain) facies association in the Salt Range and Khisor Range.In addition,a stream flow facies association is restricted to the eastern Salt Range.The alluvial plain facies association is comprised of clast-supported massive conglomerate(Gmc),diamictite(Dm)facies,and massive sandstone(Sm) Hthofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and siltstone(Fss),fining upwards pebbly sandstone(Sf),and massive mudstone(Fm) Hthofacies.The lack of glacial signatures(particularly glacial grooves and striatums) in the deposits in the Tobra Formation,which are,in contrast,present in their timeequivalent and palaeogeographically nearby strata of the Arabian peninsula,e.g.the AI Khlata Formation of Oman and Unayzah B member of the Saudi Arabia,suggests a pro-to periglacial,i.e.glaciofluvial depositional setting for the Tobra Formation.The sedimentology of the Tobra Formation attests that the Salt Range,Pakistan,occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian-Asselian time.     

大兴安岭北段伸展构造

本文对大兴安岭北段额尔古纳七卡地区发育的大型区域伸展滑脱构造开展了详细的研究,并系统地总结讨论了大兴安岭地区伸展构造及其与大兴安岭隆升的成因联系。查明七卡伸展构造带总体走向NE,滑脱面倾向NW,变形为具有减薄特征的简单剪切应变,发育SL构造岩,运动指向标志J显示向NW的伸展滑脱。结合区域上嫩江科洛伸展构造、嘎啦山伸展构造和磋岗伸展构造的对比研究表明,大兴安岭地区的伸展构造应该是区域伸展作用的产物,形成时间为早白垩世。随着大规模区域伸展作用,大兴安岭地区发生强烈的岩浆底侵,导致大兴安岭快速隆升,从而使其形成东侧向SE和西侧向NW方向滑脱的伸展构造。     

Tectonic evolution of the Brooks Range ophiolite, northern Alaska

Analysis of internal structures of the Brooks Range ophiolite at the three largest and well-exposed klippen reveals a NE–SW structural grain that may parallel the original axis of magmatism of a slow spreading marginal ocean basin. Sub-parallel directions of lattice fabrics in olivine of mantle peridotite and shape fabrics in pyroxene and plagioclase of layered gabbro indicate that asthenospheric and magmatic flow was closely coupled. These structures, including the petrologic moho, mostly dip steeply to the NW and SE, with slightly oblique flow lineations. Sedimentary and volcanic cover deposits also dip SE. The few exposures found of sheeted dike complexes generally strike parallel, but dip orthogonal to both the petrologic moho and cover deposits. These structural features are locally disturbed by syn- and post-magmatic normal faults emblematic of slow-spreading ridge processes. However, the consistent geometry of structures over a distance of 200 km demonstrates not only that the magmatic system was organized in a similar manner to an oceanic ridge, but that there was little to no rotation of individual klippe during tectonic emplacement.Ductile fabrics related to tectonic emplacement yield top-to-the NNW sense of shear indicators. The basal thrust and accompanying serpentinized shear zone is mostly flat-lying and truncates the steeply dipping ductile fabric of the ophiolite. This relationship and paleomagnetic data from the igneous sequence suggest that flow fabrics were most likely moderately inclined at the time the ophiolite formed. Similar relationships are found at diapiric centers along oceanic ridges and in other ophiolite bodies.     

The effects of fire and tephra deposition on forest vegetation in the Central Cascades, Oregon

High-resolution charcoal and pollen analyses were used to reconstruct a 12,000-yr-long fire and vegetation history of the Tumalo Lake watershed and to examine the short-term effects that tephra deposition have on forest composition and fire regime. The record suggests that, from 12,000 to 9200 cal yr BP, the watershed was dominated by an open Pinus forest with Artemisia as a common understory species. Fire episodes occurred on average every 115 yr. Beginning around 9200 cal yr BP, and continuing to the present, Abies became more common while Artemisia declined, suggesting the development of a closed forest structure and a decrease in the frequency of fire episodes, occurring on average every 160 yr. High-resolution pollen analyses before and after the emplacement of three distinct tephra deposits in the watershed suggest that nonarboreal species were most affected by tephra events and that recovery of the vegetation community to previous conditions took between 40 and 100 yr. Changes in forest composition were not associated with tephra depositional events or changes in fire-episode frequency, implying that the regional climate is the more important control on long-term forest composition and structure of the vegetation in the Cascade Range.     

Conductively driven,high‐thermal gradient metamorphism in the Anmatjira Range,Arunta region,central Australia

LA–ICP–MS in situ U–Pb monazite geochronology and P–T pseudosections are combined to evaluate the timing and physical conditions of metamorphism in the SE Anmatjira Range in the Aileron Province, central Australia. All samples show age peaks at c. 1580–1555 Ma, with three of five samples showing additional discrete age peaks between c. 1700 and 1630 Ma. P–T phase diagrams calculated for garnet–sillimanite–cordierite–K‐feldspar–ilmenite–melt bearing metapelitic rocks have overlapping peak mineral assemblage stability fields at ~870–920 °C and ~6.5–7.2 kbar. P–T modelling of a fine‐grained spinel–cordierite–garnet–biotite reaction microstructure suggests retrograde P–T conditions evolved down pressure and temperature to ~3–5.5 kbar and ~610–850 °C. The combined geochronological and P–T results indicate the SE Anmatjira Range underwent high‐temperature, low‐pressure metamorphism at c. 1580–1555 Ma, and followed an apparently clockwise retrograde path. The high apparent thermal gradient necessary to produce the estimated P–T conditions does not appear to reflect decompression of high‐P assemblages, nor is there syn‐metamorphic magmatism or structural evidence for extension. Similar to previous workers, we suggest the high‐thermal gradient P–T conditions could have been achieved by heating, largely driven by high heat production from older granites in the region.     

东秦岭二郎坪群热水沉积硅质岩的地球化学特征

东秦岭二郎坪群中广泛发育一套与铜铅锌成矿作用关系密切的硅质岩。区内硅质岩总体属于低硅质硅质岩,SiO2与Al2O3呈负相关,Fe2O3/FeO比值一般小于1,与热水沉积硅质岩的特征一致;南阳盆地以西的硅质岩MnO/TiO2比值小于0.5、Al/(Al Fe)比值接近北太平洋比值,而盆地以东的硅质岩MnO/TiO2比值大于0.5、Al/(Al Fe)比值与日本中部大陆边缘的三叠纪层纹状硅质岩比值类似;硅质岩稀土元素总量较低,重稀土元素有富集的趋势,Ce亏损较明显,Eu显示正异常,表明本区硅质岩主要是热水沉积作用的产物;硅质岩的V、Ni、Cu等微量元素含量具有洋中脊(或远洋盆地)和大陆边缘硅质岩的双重特征。     

唐古拉山冬克玛底冰川作用区的水化学特征

冬克玛底冰川附近地区是该冰川化学成分的主要来源区。冬克玛底河水及冰川上的新，老雪的矿化度，总碱度，硬度的大小顺序是：河水－老雪－－新雪。虽然它们都属淡水范畴，但新雪是性偏酸的极软水，老雪是偏碱的极软水，河水则属碱性软水。     

Late Pleistocene and Holocene glaciation of the Fish Lake valley,northeastern Alaska Range,Alaska

We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north‐eastern Alaska Range using ¹⁰Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5 ka, and then experienced a readvance or standstill at 11.6 ± 0.3 ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3–3.0 ka. A subsequent advance culminated at ca. AD 610–900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that ¹⁰Be dating from high‐elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between ¹⁰Be and lichenometric ages reveal that ¹⁰Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Field report: Exploring the Doonerak fenster of the central Brooks Range,Alaska, USA

Arctic Alaska is a ‘suspect’ terrane that encompasses approximately 20% of Alaska, stretching from the southern Brooks Range all the way to the continental shelves of the Chukchi and Beaufort Seas. Although the origin and subsequent travels of this large crustal fragment are debated among geologists, most researchers agree upon its composite nature and exotic origin. To constrain the early geological history of this terrane, we describe a recent expedition to the Doonerak fenster of the central Brooks Range. This area has long been regarded as a key locality for understanding the structural evolution of the Mesozoic–Cenozoic Brooks Range orogen; however, our target was different: a unique sequence of volcanic and siliciclastic rocks (Apoon assemblage) exposed beneath a profound pre-Mississippian unconformity, which we argue is of key importance to understanding the early Paleozoic tectonic history of northern Alaska and the greater Arctic.     

东天山黑沟流域冰川沉积序列及OSL测年研究

黑沟源于东天山最大现代冰川作用中心博格达峰的南坡. 在第四纪冰期与间冰期旋回中,该流域的冰川均发生过多次规模较大的进退,在谷中留下了较为完整的冰川沉积序列. 这些冰川地形包含有重要的古气候变化信息,对其研究可重建黑沟流域的冰川演化史. 应用OSL对该流域的冰川沉积物进行定年,测定结果表明冰水沉积物（沙质透镜体）比冰碛物更适宜应用单片再生剂量（SAR）测年技术进行测定. 基于测得的年龄并结合地貌地层学原理可初步得出：晚第四纪期间,黑沟流域共发生了5次规模较大的冰川作用,分别为全新世期间的小冰期（16世纪以来冷期的冰进）与新冰期（距今3~4 ka的冰进）,末次冰期晚冰阶（MIS 2）与早冰阶（MIS 4）以及倒数第二次冰期（MIS 6）.     

青藏高原唐古拉山北坡夏季风降水特征的初步分析

利用ＧＡＭＥ－Ｔｉｂｅｔ加强观测期间（１９９８年５￣９月）Ｄ１０５站的降水资料,初步分析了青藏高原唐古拉山北坡夏季风降水的特征。表明从６月７日到９月１８日,这１０４ｄ中有８１ｄ产生降水,总结水量为２７９．２ｍｍ,每天平均降水量达３．４５ｍｍ。可以认为６月７日左右为唐古拉山北坡Ｄ１０５站处夏季风爆发日。８月份降水量最大。为１２１．６ｍｍ,占观测期间总降水量的４３．６％。在夏季风期间,季风降水存在着明     

Petrology of sapphirine granulite and associated sodic gneisses from the Indian Head Range, Newfoundland

Migmatitic granulites from the Indian Head Range (IHR) are dominated by granoblastic, Opx-bearing (quartz) dioritic gneiss with subordinate garnet+orthopyroxene+biotite+albite (±quartz±microcline±cordierite±sillimanite) gneiss and comparatively biotite-rich, sapphirine+cordierite+orthopyroxene+albite (±microcline±sillimanite±corundum) gneiss. The latter contains at least two generations of sapphirine and cordierite, one apparently predating migmatization, the other associated with or following this event. Mineral thermobarometers yield temperatures up to 800 °C at 8 kbar. The IHR granulites have very high δ¹⁸O values (+10.8 to +14.5) which most likely indicate a sedimentary precursor. Their REE and HFSE contents resemble the trace element signature of post-Archean Australian shale (PAAS). Lithological analogues from other Grenvillian inliers in western Newfoundland have similar oxygen isotopic and immobile-element signatures. They too are interpreted as metasedimentary rocks. The IHR rocks, however, have unusually sodic compositions (e.g., Na₂O/CaO and Na₂O/K₂O=2.1–22.5 and 0.93–13.8, respectively) and contain albite or sodic oligoclase despite their high metamorphic grade. The geochemical data indicate that these rocks were albitized prior to high-grade metamorphism. No counterpart of this event is recorded in granulites from the other inliers, indicating that the IHR may be highly allochthonous with respect to these other Grenvillian terranes.     

Orientation,composition, and entrapment conditions of fluid inclusions in the footwall of the northern Snake Range detachment,Nevada

Footwall rocks of the northern Snake Range detachment fault (Hampton and Hendry's Creeks) offer exposures of quartzite mylonites (sub-horizontal foliation) that were permeated by surface fluids. An S–C–C′ mylonitic fabric is defined by dynamically recrystallized quartz and mica. Electron backscatter diffraction analyses indicate a strong preferred orientation of quartz that is overprinted by two sets of sub-vertical, ESE and NNE striking fractures. Analyses of sets of three perpendicular thin sections indicate that fluid inclusions (FIs) are arranged according to macroscopic fracture patterns. FIs associated with NNE and ESE-striking fractures coevally trapped unmixed CO₂ and H₂O-rich fluids at conditions near the critical CO₂–H₂O solvus, giving minimum trapping conditions of T = 175–200 °C and ∼100 MPa H₂O-rich FIs trapped along ESE-trending microcracks in single crystals of quartz may have been trapped at conditions as low as 150 °C and 50 MPa indicating the latest microfracturing and annealing of quartz in an overall extensional system. Results suggest that the upper crust was thin (4–8 km) during FI trapping and had an elevated geotherm (>50 °C/km). Footwall rocks that have been exhumed through the brittle-ductile transition in such extensional systems experience both brittle and crystal-plastic deformation that may allow for circulation of meteoric fluids and grain-scale fluid–rock interactions.     

Geomorphological analysis of neotectonic deformation,northern Owens Valley,California

At the western edge of the Basin and Range Province, the Owens Valley is the site of active seismicity and deformation. Morphometric analyses of three geomorphological features are used to determine the patterns and rates of neotectonic deformation: (l) a network of Pleistocene channels cut on top of the Bishop Tuff; (2) uplifted terraces of the Owens River; and (3) alluvial fans of the White Mountain front.In the Owens Valley, the three analyses are consistent with the same solution: net eastward tilt of the Owens Valley block at a rate of between 3.5 and 6.1°/Ma. Given the dip on the basement determined from geophysical data and extrapolating the rate of tilt in the Owens Valley back in time, it is inferred that the break-up of the Sierra Nevada and the northern Owens Valley occurred in the Pliocene, between around 2 and 4 Ma ago. The pattern of deformation in the northern Owens Valley matches anticlinal flexure on the Coyote warp, near the front of the Sierra Nevada, and faulting across the Volcanic Tableland is consistent with flexural extension. It is proposed that the Coyote warp is an expression of the tectonic hinge between westward rotation of the Sierra Nevada and eastward rotation of the Owens Valley since the Pliocene.     

High-pressure-low-temperature metamorphism of granitic orthogneiss in the Brooks Range, northern Alaska

Abstract Granitic orthogneiss is widespread throughout the metamorphic core of the Brooks Range in both the ductilely deformed blueschist/greenschist facies Schist Belt and the lower grade Central Belt (= Skajit allochthon) to the north. Orthogneiss occurs as large metaplutonic massifs and in small bodies enclosed within metasedimentary rocks. Crystallization ages for the granitic protoliths range from Proterozoic through Devonian (U-Pb zircon); the K-Ar system was reset during Cretaceous metamorphism. Mineral assemblages of the orthogneisses reflect nearly complete re-equilibration during Jurassic-Cretaceous collisional orogenesis in northern Alaska. The most common metamorphic paragenesis in orthogneiss is: Qtz + Kfs + Ab + Phe + Bt ± Ep, Ttn, Rt, Ap, Chl, Cal. Constituent minerals from 16 Brooks Range orthogneiss samples were analysed with the electron microprobe. Phengite from the Schist Belt samples is highly enriched in Al-celadonite, with Si values up to 3.50 per formula unit (on an 11-oxygen basis). Central Belt samples contain phengite with lower Si content (±3.38 p.f.u.). In nearly all samples, Si content of phengite varies considerably, reflecting partial re-equilibration to lower pressure and/or higher temperature conditions. Metamorphic conditions were estimated using the Phe-Bt-Kfs-Qtz barometer and the two-feldspar solvus thermometer. The results indicate that the Schist belt underwent high-pressure/low-temperature metamorphism (generally 9-12 kbar at 375-430° C), consistent with the widespread development of glaucophane + epidote/clinozoisite and lawsonite pseudomorphs in other rock types. The Central Belt also experienced a relatively high P-T metamorphism, with most samples yielding pressure estimates in the range 5-8 kbar (at 325-415° C). These results confirm the existence of two metamorphic belts in the core of the Brooks Range that differ in metamorphic conditions by up to 5 kbar. The range in Si content in phengite from Schist Belt samples is consistent with isothermal decompression of up to 5 kbar.     

藏北唐古拉山木乃花岗岩地壳隆升的裂变径迹证据

应用磷灰石裂变径迹定年,对出露于青藏高原腹地羌塘地体唐古拉山中央隆起带北坡不同高程的木乃花岗岩进行了系统的裂变径迹测年,分别获得（66．9±10．9）Ma,（66．7±16．1）Ma,（65．2±9．9）Ma,（55．8±5．4）Ma和（55．6±7．5）Ma等中值年龄;部分磷灰石裂变径迹年龄与花岗岩体的形成年龄（67．1±2．0）Ma相当,这从另一角度证明了唐古拉山木乃花岗岩形成于白垩纪末期的事实。根据青藏高原羌塘地体的古地温梯度为2．45℃／100m～2．68℃／100m,磷灰石冷却温度为110℃,求得的木乃花岗岩浆成岩深度为4100m～4500m,木乃花岗岩的平均剥蚀速率为0．061mm／a～0．081mm／a,据此推算出藏北唐古拉山木乃地区的在中生代末以来的地壳隆升幅度至少在9550m～9950117．以上．     

10Be ages of late Pleistocene deglaciation and Neoglaciation in the north‐central Brooks Range,Arctic Alaska

We present a chronology of late Pleistocene deglaciation and Neoglaciation for two valleys in the north‐central Brooks Range, Alaska, using cosmogenic ¹⁰Be exposure dating. The two valleys show evidence of ice retreat from the northern range front before ～16–15 ka, and into individual cirques by ～14 ka. There is no evidence for a standstill or re‐advance during the Lateglacial period, indicating that a glacier advance during the Younger Dryas, if any, was less extensive than during the Neoglaciation. The maximum glacier expansion during the Neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4.6 ± 0.5 and 2.7 ± 0.2 cal ka BP. Both moraine ages agree with previously published lichen‐inferred ages, and confirm that glaciers in the Brooks Range experienced multiple advances of similar magnitude throughout the late Holocene. The similar extent of glaciers during the middle Holocene and the Little Ice Age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as Neoglaciation progressed. Copyright © 2012 John Wiley & Sons, Ltd.     

Jurassic magmatism related Pb-Zn-W-Mo polymetallic mineralization in the central Nanling Range,South China: Geochronologic,geochemical, and isotopic evidence from the Huangshaping deposit

The Nanling Range in South China is characterized by extensive Mesozoic magmatism and coeval nonferrous and rare metal mineralization. Huangshaping is a world-class Pb-Zn-W-Mo polymetallic skarn deposit in the central Nanling Range. Magmatic rocks occurring in this ore district include quartz porphyry, granite porphyry, granophyre, dacite porphyry, and aplite, with only the first three granitoids genetically associated with polymetallic mineralization. Most of the orebodies are constrained within the contact zones as skarn and veins between these granitic stocks and the carbonate wall rocks.Since the age of the quartz porphyry is still controversial, and studies of the dacite porphyry and aplite are absent, we focus on these magmatic rocks first. LA-ICP-MS zircon U-Pb dating suggests that the crystallization ages of the quartz porphyry, dacite porphyry, and aplite are 154.3 ± 1.9 Ma, 158.1 ± 0.8 Ma, and 148.4 ± 3.4 Ma, respectively. Combined with previously published age data, we infer the evolutionary sequence of magmatic rocks should be dacite porphyry → quartz porphyry → granite porphyry (granophyre) → aplite. The quartz porphyry, dacite porphyry, and aplite yield high contents of high field strength elements (Zr + Nb + Ce + Y = 255–440 ppm), high ratios of 10,000 × Ga/Al (2.6–3.2), and prominent depletions in Ba, Sr, Eu, P, and Ti, indicating their crustal affinities to A-type granites. They have negative ε_Nd(t) values (−9.4 to −7.0) and high initial Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb_i = 18.307–18.644, ²⁰⁷Pb/²⁰⁴Pb_i = 15.689–15.742, ²⁰⁸Pb/²⁰⁴Pb_i = 38.589–38.986), suggesting that they were probably derived by partial melting of ancient granulitic crustal materials.The sulfide minerals exhibit a wide range of δ³⁴S_V-CDT values from −22.6 to 24.2‰, with ²⁰⁶Pb/²⁰⁴Pb of 17.669–19.708, ²⁰⁷Pb/²⁰⁴Pb of 15.492–15.714, and ²⁰⁸Pb/²⁰⁴Pb of 37.880–39.789, indicating that sulfur, lead, and other associated metals were derived from a mixture of magmatic components and the Carboniferous wall rocks. Fluid inclusions in pyrrhotite, sphalerite, and marmatite samples have ³He/⁴He ratios of 0.12 to 1.53 Ra, with calculated mantle helium proportions of 1.3 to 18.9%, indicating a predominantly crustal origin for the ore fluids, with minor inputs from the mantle. The Huangshaping deposit is a typical example of the genetic relationship both spatially and temporally between Jurassic magmatism and polymetallic metallogeny in the Nanling Range.     

Geology, mineralogy, and PGE mineralization of the copper-nickel occurrences of the Kvinum ore field, Sredinny Range, Kamchatka

The geology and mineralogy of host metamorphic rocks, the mineralogy of sulfide ores, and the distribution of PGE mineralization were studied in detail for the Kvinum-1 and Kvinum-2 copper-nickel occurrences of the Kvinum ore field, which are the most promising targets for the copper-nickel-PGE mineralization of the Sredinny Range of Kamchatka. It was established that stringer-disseminated and massive copper-nickel ores are localized in amphibole peridotites, cortlandites, and form ore bodies varying from tens of centimeters to 5–20 m thick among the layered cortlandite-gabbroid massifs. The massive sulfide ores were found only at the bottom of cortlandite bodies and upsection grade into stringer-disseminated and disseminated ores. Pyrrhotite, chalcopyrite, and pentlandite are the major ore minerals with a sharply subordinate amount of pyrite, sphalerite, galena, arsenopyrite, and löllingite. Besides pentlandite, the Ni-bearing minerals include sulforasenides (gersdorffite), arsenides (nickeline), and tellurides (melonite) of nickel. It was found that PGE mineralization represented by antimonides (sudburyite) and tellurobismuthides (michenerite) of Pd with sharply subordinate platinum arsenide (sperrylite) is confined to the apical parts of massive sulfide zones and the transition zone to the stringer-disseminated ores. Ore intervals enriched in arsenides and tellurides of Ni, Pd, and Bi contain high-purity gold. In the central parts of the orebodies, the contents of PGE and native gold are insignificant. It is suggested that the contents of major sulfide minerals and the productivity of PGE mineralization in the cortlandites are defined by combined differentiation and sulfurization of ultramafic derivatives under the effect of fluids, which are accumulated at the crystallization front and cause layering of parental magmas with different sulfur contents. The fluid-assisted layering of mafic-ultramafic massifs resulted in the contrasting distribution of PGM in response to uneven distribution of sulfur (as well as As, Te, and Bi) during liquid immiscibility. The productivity of PGE mineralization significantly increases with increasing contents of S, As, Te, and Bi (elements to which Pt and, especially, Pd have high affinity) in fluids.