The behaviour of platinum-group elements (PGE: Ir, Os, Rh, Ru, Pd and Pt) on a nano level may be the key to the enrichment of PGE in mafic ore bodies, like the Bushveld complex. Temperature controlled sulphide melts were used to investigate possible PGE-rich nano phases or clusters, in a magmatic environment, and the influence these structures may have on PGE enrichment. The sulphide portion of a natural Cu-Ni-S ± PGE system was mimicked experimentally. Sulphides are of the first minerals to form in a magmatic system and more likely to carry PGE-clusters. Samples were prepared using the dry powder silica tube technique. The starting powders consisted of a base mixture of an S, Cu and Fe. These were doped with variable concentration of PGE (either Pt or Pd or Ru) and chalcogene ligand (As). The samples were cooled at different rates to monitor the influence of environmental changes (time, chemistry, kinematic- and thermodynamic) on possible cluster formation. A variety of primary and secondary nano structures (<100nm) were measured in the synthetic samples, using semi-quantitative scanning Auger microscopy (SAM). The size, morphology and composition of the nano entities were a function of the PGE-system (chemistry) and allowed cooling time. The structures formed irrelevant of the PGE concentration. Several of the identified nano structures were re-classified as potential PGE-clusters. These structures fall within the size range of clusters (10-100nm) and were a good indication whether clusters could form. Although no conclusive clusters were measured evidence from time of flight secondary ion mass spectrometry (TOF-SIMS) analysis supported the notion that the PGE can form PGE-ligand agglomerations of 10-100nm. Scans showed irregular distribution of PGE-ligand ion bundles in compatible and incompatible phases. The PGE-ligand bundles were conclusive evidence that potential clusters can stay preserved in a system with changes in environment. If this interpretation is correct, it might indicate that a physical enrichment process is at work during the early stages of crystallization in a magmatic environment. However clustering is only one of several mechanisms that may contribute to PGE enrichment of Bushveld-type deposits

Not available

The Ventersburg Project is located in the Free State Goldfields south of the town of Hennenman. The A Reef particularly its stratigraphic and sedimentological character is the subject of study in the project area. The reef occurs stratigraphically in the Aandenk Formation of the Central Rand Group, Witwatersrand Supergroup, South Africa. The A Reef occurs a few meters below the angular unconformity underlying the Eldorado Basal Conglomerate and above an unconformity surface between the Spes Bona and Aandenk Formations. The fact that most Witwatersrand placers occur on unconformity surfaces is well known throughout the Witwatersrand Basin (Phillips and Law, 2000). The A Reef in the project area is a low grade, shallow ore body (less than 1000 meters below surface). Intersections of the A Reef from borehole core were used to determine the facies and sub-environments. The A Reef placer is distinctly different from the underlying polymictic Big Pebble Marker comprising mature, oligomictic, small to medium pebble conglomerates and siliceous quartzites showing upwards fining cycles, typical of braided alluvial plain environments. Sediment transport directions towards the east-south-east are similar to those in the Free State Goldfields. Channels of the A Reef are highly complex, occurring in large channel complexes of more than 500 meters wide with individual smaller channels of 200 to 500 meters wide. The A Reef in the northern part of the project area is separated from the underlying Big Pebble Marker by between 1 to 3 meters of argillaceous quartzwacke. To the south, the A Reef is directly on top of the Big Pebble Marker. Mineralisation in the A Reef decreases to the south where it sub-outcrops against the Eldorado Basal Conglomerate and only localised higher gold grades occur within the Big Pebble Marker. At increased high gold prices, previously uneconomic ore bodies can become renewed targets for exploration in the near future.

Although the Thettord-Black Lake District has received considerable attention the past, a great deal of information, of geological value has become available during the past twenty years as a result of the progress made in the mining and intensive exploration. The area chosen was intended to include all of the major intrusive bodies of this locality; however, a five minute strip along the eastern side still remains to be mapped before this objective may be considered to have been achieved. Nevertheless, all of the asbestos deposits lie within the portion already mapped, and all of the intrusive rock types are present in this portion.

The southern Highland Mountains, located in southwest Montana, contain a diverse assemblage of high-grade metamorphic rocks cored by migmatized leucocratic orthogneiss, with garnet-sillimanite paragneiss and schist at structurally higher levels. Based on the structure of the metamorphic rocks, ONeill et al. (1988) hypothesized that the southern Highland Mountains is a gneiss dome. This study evaluates the gneiss dome hypothesis by conducting a petrologic study of the metamorphic rocks in the southern Highland Mountains using thin section analysis and pseudosections to determine if spatial trends in metamorphic conditions consistent with those of gneiss domes exist. In total, six samples were selected for P-T analysis. Pseudosections were constructed using the program Theriak/Domino with the internally consistent thermodynamic database of Holland and Powell (1998) in the system Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe¬2O3 (NCKFMASHTO). Of the six pseudosections, four are of metapelitic rocks with the assemblage garnet + sillimanite + biotite + plagioclase + potassium feldspar + ilmenite + quartz, one is an orthoamphibolite with the assemblage garnet + orthopyroxene + biotite + anthophyllite + plagioclase + ilmenite + rutile + quartz, and one is an amphibolite with an assemblage of garnet + biotite + hornblende + plagioclase + ilmenite + quartz. Petrographic analysis in conjunction with pseudosections reveals a prograde clockwise pressure-temperature (P-T) path with peak metamorphic conditions ranging from 8.6 to 9.6 kbar and 750 to 840 °C. The P-T path for the metapelitic rocks went through the kyanite stability field before stabilizing within the sillimanite stability field. A lack of a significant change in P-T conditions from core to flanks suggests that the metamorphic evolution of these rocks is not consistent with the gneiss dome hypothesis. When the metamorphic conditions of the southern Highland Mountains are compared to those of the surrounding mountain ranges (the Tobacco Root Mountains, Ruby Range, and Gravelly Range), a succession of progressively decreasing pressures and temperatures is observed from north to south. This succession suggests that the metamorphic rocks in these mountains ranges represent a nearly continuous stratigraphic exposure of rocks from the metamorphic core of a regional scale thermotectonic event called the Big Sky orogeny.

<p> The Little Pine fault (LPF) delineates the northeast margin of the Santa Maria Basin. The basin is inverting due to north-northeast, south-southwest shortening, associated with vertical-axis rotation of the western Transverse Ranges to the south. Slip data collected along the Little Pine fault yielded principle compressive stress directions that are indicative of reverse slip, with minor lateral components that vary along strike of the fault. Slip data collected to the northwest along the Foxen Canyon fault is indicative of right lateral strike-slip. Mapped offsets near Coralles, Happy, and Cachuma canyons indicate 228 meters of reverse offset across the LPF south branch since Pliocene time. The LPF is segmented, with segments exhibiting different histories. Based on mapped offsets of contacts between Miocene units near Foxen canyon, the rate of dextral slip along the Foxen Canyon fault is 0.027 to 0.1 millimeters per year from Miocene to Pliocene.</p>

<p> The activity of the Ereen Uul fault and the Sanglin Dalai Nurr fault in central Mongolia has not been studied in detail. The Erren Uul fault is a normal fault located 45 km southeast from Harhorin and the Sanglin Dalai Nurr fault is a right-lateral strike-slip fault located 30 km south of Harhorin next to the Hangay Mountains. Remote sensing and field observations were used to refine a map by the Mongolian Geologic Survey at a scale of 1:1,000,000 to a scale of 1:100,000. This new map covers an area of 8,072 km². The basin asymmetry factor, stream length-gradient index, and hypsometric curves were developed for basins adjacent to these faults. These geomorphic indices along with the refined map were used to conclude that the Ereen Uul and Sanglin Dalai Nurr faults are active.</p>

<p> The ~5.6-4.8 Ma Bouse Formation, exposed along the lower Colorado River, contains a well exposed but debated record of river integration. Sedimentologic and stratigraphic analysis aid interpretation of depositional processes, relative water depth, depositional environments, stratal architecture, and basin-filling history. Data collected include detailed measured sections, facies descriptions, and fault measurements. Seven lithologically distinct units have been identified along with numerous marine sedimentary structures and fossils. The Bouse Formation preserves a systematic sequence-stratigraphic architecture that records two cycles of base level rise and fall. Lacustrine versus estuarine interpretation remains elusive, though new isotope and micropaleontology data suggest a shift from marine to lacustrine. Constructed stratigraphic facies panels reveal a wedging geometry indicative of syn- to post-depostional tilting, leading us to propose a "sag basin" model during deposition of the Bouse. Finally, the newly described Bouse upper limestone unit resolves a long-standing debate over the age of the first through-going river.</p>

Ultrapotassic, potassic alkaline and shoshonitic magmatism with subduction-related affinity co-existed in a Proterozoic (1089 to 1076 Ma) plutonic environment: the SW Grenville Province. The stocks have silica-saturated and undersaturated, felsic-to-ultramafic units emplaced diapirically in separate, progressively more mafic batches of magma. Most magmas crystallized in situ, and were saturated in apatite, biotite and clinopyroxene. Fractionation of these minerals from a single parental mafic magma is ruled out as the fractionation process prior to emplacement during which Ba, Sr, Nb and Zr were incompatible. Felsic magmas in endoskarns have been contaminated by marble. The paragenesis, the primary LILE, Ca and Al enrichment, and depletion of Nb and Ta typical of ultrapotassic rocks of island-arc, the NE-trend and SE-younging of this belt suggest active NE-trending, SE-dipping subduction during this episode of magmatism and are used to delimit allochthonous terranes.

The Grey River Area lies on the south coast of Newfoundland. In general, it includes the land between Grey River and Haie de Vieux, lat. 470 40’ - 47°50’, long. 51’001 - 57°15 1. The area may be reached by steamer, which runs weekly between Port aux Basques and Argentia. The nearest major settlement is Burgeo, 24 miles west along the coast; Ramea, a minor fishing port lies 12 miles southwest on Ramea Island. The Grey River area is 87 miles due south of Buchans. It is accessible from the air, and both Grey River and Long Pond have adequate facilities for landing small sea planes. The Grey River fishing settlement lies on Grey River, about half a mile from the open sea. It is built on a small triangular alluvial cone, about 400 by 600 feet in dimension, inhabited by 30 families, with a total population of 250. The settlement is bordered on two sides by cliffs, which rise steeply to 800 feet above sea level. Inland, the country is uninhabited. / fr