The lower part of the post-Variscan succession around Exeter, south Devon, England, comprises some 800 m of breccias, with subordinate sandstones and mudstones, which rest upon Devonian and Carboniferous rocks folded during the Variscan Orogeny and are overlain, disconformably, by the Aylesbeare Mudstone Group (Early Triassic?). These deposits comprise the most westerly of the early post-Variscan successions preserved onshore in northwest Europe and lie to the south of the Variscan Deformation Front; they are assigned to the Exeter Group (new term). Geochronological and palaeontological studies, in conjunction with detailed geological mapping, show that the constituent formations comprise a lower (Late Carboniferous(?)-Early Permian) sequence separated from an upper (Late Permian) sequence by an unconformity which represents an hiatus with a duration of at least 20 m.y. The lower sequence contains volcanic rocks dated at between 291 and 282 Ma (Early Permian) and pre-dates intrusion of the nearby Dartmoor Granite (280 Ma). In the overlying, palynologically-dated, Late Permian sequence, older breccias contain clasts of the Dartmoor Granite aureole rocks, and younger ones contain clasts of that granite. The lower sequence occurs mainly within the Crediton Trough, an east-west trending, partly fault-bounded, sedimentary basin that probably formed by extensional reactivation of a Variscan thrust. Breccias in this sequence formed largely on alluvial fans; the common occurrence of debris flows and a down-fan passage from gravity flows into fluvially deposited sediments is typical of deposition on semi-arid fans. The upper (Late Permian) sequence is more widespread but includes similar deposits overlain, at the top of the Exeter Group, by aeolian dune and interdune deposits. Correlation within the laterally variable facies associations which comprise these sequences has been achieved using a combination of sedimentary facies analysis, sedimentary geochemistry, and petrographical and geochemical clast typing. The stratigraphy revealed within the Exeter Group is broadly comparable with that recognized in the early post-Variscan Rotliegend successions elsewhere in Europe. This similarity may, however, be deceptive; the upper part of the Exeter Group may be coeval with the Zechstein, and apparently correlatable major unconformities in the group and the Rotliegend may reflect different events in the Variscan fold-belt and Variscan Foreland areas, respectively.

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A h c k Stratabound scheelite mineralization has been discovered in the Hindu Kush range of northern Pakistan as a result of a geochemical drainage survey. The mineralization occurs predominantly in clinozoisite-bearing calcsilicate quartzite beds within a sequence of mica schist and subordinate graphitic phyllite, mica quartzite, tourmalinite and feldspathic gneiss, but not in adjacent calcite marble. The sequence is intruded by a small leucogranite stock emplaced after the climax of Barrovian-type metamorphism during the later of two deformation phases which are related to continent-arc collisions in the Cretaceous and Eocene. In the calcsilicate quartzites, scheelite crystallized simultaneously with clinozoisite prior to the leucogranite emplacement and is clearly of metamorphic origin. Tungsten-rich brines, generated from hot springs in an extensional tectonic environment, are thought to have been concentrated in the relatively porous precursor of the calcsilicate quartzite during diagenesis. Subsequent metamorphism recrystallized the tungsten as scheelite along with metamorphic silicate minerals and caused limited mobility of the element into veins.

SUMMARY. Banded gneisses and migmatites in the Champira Dome contain assemblages of the biotitecordierite-almandine subfacies of the granulite facies. The banded gneisses represent a sequence of arkosic sediments metamorphosed to sillimanite-cordierite gneisses. The migmatites were derived from more argillaceous and potassic sediments, with lower oxidation ratios and lower Ba/Rb ratios. They consist of a quartzo-feldspathic leucosome, representing anatectic melt, with schlieren of the refractory minerals sillimanite, garnet, biotite, and oxide minerals. Cordierite developed from garnet and biotite, except in rocks of high FeO/(FeO + MgO) ratio. Both rock types contain assemblages of magnetite+ hercynite + corundum + ilmenite + hematite, formed by unmixing of high-temperature solid solutions. Rb-Sr studies of the banded gneisses gave an age of 2327 + 25 Ma, which is interpreted as the date of metamorphism, and an initial 878r/86Sr ratio of o.7o64 + 0.ooo3. The migmatite samples plot close to this 2327 Ma regression line, but the strontium isotopes were considerably disturbed, though not homogenized on the scale of sampling, 962 + 34 Ma ago. It is considered that the anatexis in the migmatites was contemporaneous with the metamorphism of the banded gneisses and that the 962 + 34 Ma event may be correlated with recrystallization of the migmatites accompanying the growth of cordierite. THE Champira Dome ( fig. IA) consists largely of banded sillimanite-cordierite garnet gneisses. It was emplaced as a tectonic wedge between ENEtrending boundary faults and appears to have a different structural and metamorphic history to that of the surrounding rocks (Peters,.i975). The purpose of this paper is to elucidate as far as possible the origins and metamorphic history of the rocks of the dome. Two suites of specimens were examined. Specimens MB 52 and 54-59 are banded gneisses. To the north-east of these ( fig. z B) is an area of migmatite . Both suites contain mineral assemblages characteristic of the

Stratiform Zn-Pb mineralization of probable Proterozoic age occurs in a structurally complex area near the northern margin of the Indian plate around Besham in the North West Frontier Province of Pakistan. The sphalerite and galena mineralization is associated with a well-defined stratigraphy of carbonate, layered calc-silicate quartzite, garnet-bearing quartzo-feldspathic gneiss, feldspathic granulite and albite gneiss. Associated with the ore are varying proportions of pyrrhotite, pyrite, baryte, clinopyroxene, quartz, garnet, actinolite, pyroxmangite, feldspar, carbonate and magnetite. The Mn-rich composition of the silicate minerals and the widespread enrichment of Ba in the rocks associated with the ore form a distinctive signature of the mineralization recognizable in reconnaissance exploration. This signature is distinct from that of skarn minerals formed later in carbonate rocks as a result of the intrusion of pegmatites. The recognition of the stratiform nature of the deposits within a well-defined stratigraphy enhances the exploration potential of the mineralization over a much wider area.