Speech Communication

Contains table of contents for Part IV, table of contents for Section 1 and reports on five research projects.Apple Computer, Inc.C.J. Lebel FellowshipNational Institutes of Health (Grant T32-NS07040)National Institutes of Health (Grant R01-NS04332)National Institutes of Health (Grant R01-NS21183)National Institutes of Health (Grant P01-NS23734)U.S. Navy / Naval Electronic Systems Command (Contract N00039-85-C-0254)U.S. Navy - Office of Naval Research (Contract N00014-82-K-0727

Uranium deposits of the Mount Isa region and their relationship to deformation, metamorphism, and copper deposition

The Mount Isa region contains over 20 uranium deposits, few of which contain economic concentrations of uranium. They are thought to be significant in the exploration for new copper deposits, based on the model that the uranium deposits are located in the pathways of oxidized hydrothermal fluids that formed the postmetamorphic Mount Isa copper orebodies.\ud \ud There are two uranium deposit types, both hosted in volcanosedimentary rocks. We suggest that they represent one mineralization event but different metamorphic histories. Examples in the eastern low-grade metamorphic zone are dominated by a brannerite-anatase-apatite assemblage and are low in uranium. The examples in the western high-grade metamorphic zone are characterized by uraninite and titanite with higher uranium concentrations. The chemical association of U, Ti, and Ca is consistent for all deposits; however, phosphate is only important at low metamorphic grade.\ud \ud The most likely mechanism of formation in the lower metamorphic grade Anderson’s Lode example is the complete replacement of chlorite in the sedimentary host-rock matrix by the mineralizing assemblage. In this model, chlorite acted as a reductant, allowing the deposition of uranium from an oxidized fluid. This mechanism of uranium deposition is similar to that proposed for unconformity-type uranium deposits. We conclude that these uranium deposits are metamorphosed equivalents of Proterozoic unconformity-type uranium deposits found elsewhere in northern Australia.\ud \ud At Anderson’s Lode, brannerite and apatite were concentrated in veinlets by pressure dissolution after the deposition of the original assemblage. These pressure dissolution seams are cut by premetamorphic quartz-chlorite veins. Examples at higher metamorphic grade have textures that suggest uranium deposition was pre- to synmetamorphic at the latest. This precludes any genetic or temporal connection between the uranium deposits and the postmetamorphic Mount Isa copper deposit

Significance of strain localization and fracturing in relation to hydrothermal mineralization at Mount Isa, Australia

The rheology of layered meta-sedimentary rocks, and their orientation and position relative to major fault systems were the key controls on Proterozoic hydrothermal copper mineralization at Mount Isa, Australia. Compositional layering in the host rock partitioned mechanical behavior and strain, leading to selective permeability generation and the focusing of fluid flow. Shale layers preferentially failed by plastic shearing, whereas meta-siltstones remained elastic or failed in tension depending on magnitude of deformation and fluid pressure. Numerical simulations support the hypothesis that the orientation of layering and the proximity to major fault systems controlled fracturing and permeability increase in the Urquhart shale. The dilating shale provided a pathway for an upward-flowing, reduced basement fluid, from which quartz was precipitated during cooling. During a later event, the reactivation of steep structures provided access to surface derived oxidized metal-bearing brine, causing the precipitation of dolomite followed by chalcopyrite ore in the brecciated silicified shale

Rhenium-osmium systematics of the Mount Isa copper orebody and the Eastern Creek Volcanics, Queensland, Australia : implications for ore genesis

The syn-tectonic breccia-hosted Mount Isa Cu deposit in northwest Queensland is the largest sediment-hosted Cu deposit in Australia. Whole-rock samples of chalcopyrite-rich Cu ore form an isochron with a Re–Os age of 1,372 ± 41 Ma. This age is more than 100 Ma younger than the previously accepted age of Cu ore formation, an Ar–Ar mineral age for biotite separated from the host rocks within the alteration envelope to the Cu orebody. This discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for Cu mineralisation or the deformation event associated with Cu emplacement. The 1,372 ± 41 Ma date may reflect (a) the time of Cu deposition, (b) the time of a hydrothermal event that reset the Re–Os signature of the Cu ore or (c) mixing of the Re–Os isotope systematics between the host rocks and Cu-bearing fluids. However, a range of published Ar–Ar and Rb–Sr dates for potassic alteration associated with Cu mineralisation also records an event between 1,350 and 1,400 Ma and these are consistent with the 1,372 Ma Re–Os age. The 1.8 Ga Eastern Creek Volcanics are a series of tholeiitic basalts with a primary magmatic Cu enrichment which occur adjacent to the Mount Isa Cu deposit. The whole-rock Os isotopic signature of the Eastern Creek Volcanics ranges from mantle-like values for the upper Pickwick Member, to more radiogenic/crustal values for the lower Cromwell Member. The Re–Os isotope signature of the Cu ores overlaps with those calculated for the two volcanic members at 1,372 Ma; hence, the Os isotope data are supportive of the concept that the Os in the Cu ores was sourced from the Eastern Creek Volcanics. By inference, it is therefore postulated that the Eastern Creek Volcanics are the source of Cu in the Mount Isa deposit, as both Os and Cu are readily transported by oxidised hydrothermal fluids, such as those that are thought to have formed the Cu orebody. The Pickwick Member yields a Re–Os isochron age of 1,833 ± 51 Ma, which is within error of previously reported age constraints. The initial ¹⁸⁷Os/¹⁸⁸Os isotopic ratio of 0.114 ± 0.067 (γOs = −0.7) is slightly subchondritic, and together with other trace element geochemical constraints, is consistent with a subcontinental lithospheric mantle source. The Pickwick Member records a minimum age of ca. 1.95 Ga for melt depletion in the subcontinental lithospheric mantle beneath the Mount Isa Inlier prior to the extraction of the magmas which formed the Eastern Creek Volcanics. This corresponds with the end of subduction-related magmatism along the eastern margin of the Northern Australian Craton, which included the Mount Isa Inlier.21 page(s

Mutations in the Gene Encoding the Sigma 2 Subunit of the Adaptor Protein 1 Complex, AP1S2, Cause X-Linked Mental Retardation

In a systematic sequencing screen of the coding exons of the X chromosome in 250 families with X-linked mental retardation (XLMR), we identified two nonsense mutations and one consensus splice-site mutation in the AP1S2 gene on Xp22 in three families. Affected individuals in these families showed mild-to-profound mental retardation. Other features included hypotonia early in life and delay in walking. AP1S2 encodes an adaptin protein that constitutes part of the adaptor protein complex found at the cytoplasmic face of coated vesicles located at the Golgi complex. The complex mediates the recruitment of clathrin to the vesicle membrane. Aberrant endocytic processing through disruption of adaptor protein complexes is likely to result from the AP1S2 mutations identified in the three XLMR-affected families, and such defects may plausibly cause abnormal synaptic development and function. AP1S2 is the first reported XLMR gene that encodes a protein directly involved in the assembly of endocytic vesicles