The hydrothermal reactivity of a Mg-vermiculite from Santa Olalla (Spain) was studied experimentally at 150 and 300ºC, 75 and 100 bars, respectively, in (Na,K,Ca,Mg) chloride and sulphate solutions (liquid/solid ratio = 10). The formation of mixed-layer clays is demonstrated by FT-IR spectroscopy, X-ray diffraction (XRD) and electron microprobe. The gradual decrease of the 3220 cm–1 infrared band intensity, characteristic of free water, is interpretated as the dehydration of the interlayer Mg cation of the vermiculite. The presence of ‘brucite type’ sheets is also observed by the increase of 3555 cm–1 and 3420 cm–1 band intensities. The XRD results show that run products are able to expand when glycolated. Microprobe analyses document the decrease of IVSi content and a significant enrichment in Mg in the run products. The formation of a mixed-layer clay comprising saponite and chlorite layers is proposed.

Arhbarite was described in 1982 as a new copper arsenate, Cu2(OH)AsO4·6H2O, from the Arhbar mine, Morocco. Due to the very small grain size no crystallographic data other than the X-ray powder diffraction data could be given. Reinvestigation of the type material and of new finds from the El Guanaco mine, Chile, is based on Rietveld refinement of X-ray powder data, electron microprobe investigations, optical studies as well as infrared and Raman spectra. The main results are: (1) arhbarite has the ideal formula Cu2Mg(AsO4)(OH)3 with magnesium oxide as an additional constituent and (2) arhbarite is isotypic with gilmarite, Cu3(AsO4)(OH)3. Arhbarite is triclinic, space group P1 (no. 1), unit-cell parameters (type material; refined from powder data) a= 5.315(4), b= 5.978(6), c= 5.030(6)Å, α = 113.58(6), β = 97.14(7), γ = 89.30(8)°, V= 145.2(1)Å3, Z= 1. Microprobe analyses of the type material gave MgO 10.20, CuO 47.46, NiO 0.20, CoO 0.24, As2O5 33.85, SiO2 0.10, H2O 7.58 (calc.), total 99.63 wt.%. The empirical formula is Cu1.98(Mg0.88Cu0.09Ni0.01Co0.01)S0.99(AsO4)1.02(OH)2.92, based on 7 O atoms. The Chilean arhbarite shows a slightly higher Cu content than the type material; it has the formula Cu1.99(Mg0.73Cu0.25Zn0.01)∑0.99[(AsO4)1.01(SiO4)0.01]∑1.02(OH)2.92. The formal redefinition of arhbarite has been approved by the CNMMN of the IMA.

The Loch Shin monzogranite is host to quartz veins bearing the sulphosalts aikinite, hammarite, lindströmite, krupkaite, gladite and pekoite, which belong to the aikinite-bismuthinite series, and represents the first significant occurrence of this series in the United Kingdom. Inclusions of the sulphotelluride tetradymite occur in krupkaite-gladite. Berryite is present as inclusions in chalcopyrite. Electron microprobe analyses reveal a range of compositions in individual crystal masses from hammarite to krupkaite in one sample, and from krupkaite to gladite in a second. Compositions between friedrichite and hammarite and gladite and pekoite are notably absent.

The Miocene Baltoro granite forms a massive plutonic unit within the Karakoram batholith, and is composed of comagmatic monzogranites and leucogranites with a mineralogy consisting of quartz-K-feldspar-plagioclase-biotite ± muscovite ± garnet, with accessory sphene, zircon, monazite and opaques. Geochemically the Baltoro granites are mildly peraluminous, and show a calc-alkaline trend on trace-element normalised diagrams with high LIL/HFS element ratios and negative Nb, P and Ti anomalies. REE are strongly fractionated with little or no Eu anomaly. Leucogranites are depleted in most elements compared to monzogranites with notable exceptions being Rb, K and the HREEs. Initial 87Sr/86Sr ratios are 0·7072-0·7128, considerably lower than High Himalayan leucogranites (0·74-0·79), and are indicative of a lower continental crust source. The probable petrogenesis of the Baltoro granite involves dehydration melting of a biotite-rich pelite to produce a voluminous, hot, water-undersaturated magma which could then separate from its source and intrude through an already thickened and still hot crust. Fractional crystallisation of the monzogranites produced the leucogranites and a pegmatite dyke swarm. A suite of lamprophyre dykes including amphibolerich vogesites and biotite-rich minettes intrude the country rock, dominantly to the north, around the Baltoro granite. These calc-alkaline shoshonitic lamprophyres are volatile-rich mantle-derived melts intruded around the same time as the granite, indicating simultaneous melting of the mantle and lower crust beneath the Karakoram during the Miocene, approximately 30 Ma after the India-Asia collision which initially caused the crustal thickening. Intrusion of mantle melts provided heat to promote crustal melting and may have selectively contaminated the granite magma.

The Baltoro granite intrudes sillimanite gneisses with melt pods along the southern margin indicating temperatures above 700°C at the time of intrusion. Locally, internal fabrics and numerous aligned xenoliths along the southern margin in the Biafo glacier region indicate steep, southward-directed thrusting during emplacement. Along the northern contact, the Baltoro granite intrudes anchimetamorphic to greenschist facies metasedimentary rocks with an andalusite-bearing contact aureole. Northward-directed culmination collapse normal faulting during Miocene emplacement is inferred, in order to explain the P-T differences either side of the pluton. This also provided an extensional stress regime in the upper crust to accommodate the rising magma.