Different mineralization styles in a volcanic-hosted ore deposit: the fluid and isotopic signatures of the Mt Morgan Au-Cu deposit, Australia

Quantitative laser ablation (LA)-ICP-MS analyses of fluid inclusions, trace element chemistry of sulfides, stable isotope (S), and Pb isotopes have been used to discriminate the formation of two contrasting mineralization styles and to evaluate the origin of the Cu and Au at Mt Morgan. The Mt Morgan Au-Cu deposit is hosted by Devonian felsic volcanic rocks that have been intruded by multiple phases of the Mt Morgan Tonalite, a low-K, low-Al2O3 tonalite-trondhjemite-dacite (TTD) complex. An early, barren massive sulfide mineralization with stringer veins is conforming to VHMS sub-seafloor replacement processes, whereas the high-grade Au-Cu. ore is associated with a later quartz-chalcopyrite-pyrite stock work mineralization that is related to intrusive phases of the Tonalite complex. LA-ICP-MS fluid inclusion analyses reveal high As (avg. 8850 ppm) and Sb (avg. 140 ppm) for the Au-Cu mineralization and 5 to 10 times higher Cu concentration than in the fluids associated with the massive pyrite mineralization. Overall, the hydrothermal system of Mt Morgan is characterized by low average fluid salinities in both mineralization styles (45-80% seawater salinity) and temperatures of 210 to 270 degreesC estimated from fluid inclusions. Laser Raman Spectroscopic analysis indicates a consistent and uniform array Of CO2-bearing fluids. Comparison with active submarine hydrothermal vents shows an enrichment of the Mt Morgan fluids in base metals. Therefore, a seawater-dominated fluid is assumed for the barren massive sulfide mineralization, whereas magmatic volatile contributions are implied for the intrusive related mineralization. Condensation of magmatic vapor into a seawater-dominated environment explains the CO2 occurrence, the low salinities, and the enriched base and precious metal fluid composition that is associated with the Au-Cu. mineralization. The sulfur isotope signature of pyrite and chalcopyrite is composed of fractionated Devonian seawater and oxidized magmatic fluids or remobilized sulfur from existing sulfides. Pb isotopes indicate that Au and Cu. originated from the Mt Morgan intrusions and a particular volcanic strata that shows elevated Cu background. (C) 2002 Elsevier Science B.V. All rights reserved.

Ductile fabrics in the zone of active oblique convergence near the Alpine Fault, New Zealand: identifying the neotectonic overprint

The mid-crustal Alpine Schist in central Southern Alps, New Zealand has been exhumed during the past similar to3 m.y. on the hanging wall of the oblique-slip Alpine Fault. These rocks underwent ductile deformation during their passage through the similar to 150-km-wide Pacific-Australia plate boundary zone. Likely to be Cretaceous in age, peak metamorphism predates the largely Pliocene and younger oblique convergence that continues to uplift the Southern Alps today. Late Cenozoic ductile deformation constructively reinforced a pre-existing fabric that was well oriented to accommodate a dextral-transpressive overprint. Quartz microstructures below a recently exhumed brittle-ductile transition zone reflect a late Cenozoic increment of ductile strain that was distributed across deeper levels of the Pacific Plate. Deformation was transpressive, including a dextral-normal shear component that bends and rotates a delaminated panel of Pacific Plate crust onto the oblique footwall ramp of the Alpine Fault. Progressive ductile shear in mylonites at the base of the Pacific Plate overprints earlier fabrics in a dextral-reverse sense, a deformation that accompanies translation of the schists up the Alpine Fault. Ductile shear along that structure affects not only the 12-km-thick section of Alpine mylonites, but is distributed across several kilometres of overlying nonmylonitic rocks. (C) 2001 Elsevier Science Ltd. All rights reserved.

Blast design using measurement while drilling parameters

Measurement while drilling (MWD) techniques can provide a useful tool to aid drill and blast engineers in open cut mining. By avoiding time consuming tasks such as scan-lines and rock sample collection for laboratory tests, MWD techniques can not only save time but also improve the reliability of the blast design by providing the drill and blast engineer with the information specially tailored for use. While most mines use a standard blast pattern and charge per blasthole, based on a single rock factor for the entire bench or blast region, information derived from the MWD parameters can improve the blast design by providing more accurate rock properties for each individual blasthole. From this, decisions can be made on the most appropriate type and amount of explosive charge to place in a per blasthole or to optimise the inter-hole timing detonation time of different decks and blastholes. Where real-time calculations are feasible, the system could extend the present blast design even be used to determine the placement of subsequent holes towards a more appropriate blasthole pattern design like asymmetrical blasting.

Asymmetric blasting: a rock mass dependent blast design method

Blasting has been the most frequently used method for rock breakage since black powder was first used to fragment rocks, more than two hundred years ago. This paper is an attempt to reassess standard design techniques used in blasting by providing an alternative approach to blast design. The new approach has been termed asymmetric blasting. Based on providing real time rock recognition through the capacity of measurement while drilling (MWD) techniques, asymmetric blasting is an approach to deal with rock properties as they occur in nature, i.e., randomly and asymmetrically spatially distributed. It is well accepted that performance of basic mining operations, such as excavation and crushing rely on a broken rock mass which has been pre conditioned by the blast. By pre-conditioned we mean well fragmented, sufficiently loose and with adequate muckpile profile. These muckpile characteristics affect loading and hauling [1]. The influence of blasting does not end there. Under the Mine to Mill paradigm, blasting has a significant leverage on downstream operations such as crushing and milling. There is a body of evidence that blasting affects mineral liberation [2]. Thus, the importance of blasting has increased from simply fragmenting and loosing the rock mass, to a broader role that encompasses many aspects of mining, which affects the cost of the end product. A new approach is proposed in this paper which facilitates this trend 'to treat non-homogeneous media (rock mass) in a non-homogeneous manner (an asymmetrical pattern) in order to achieve an optimal result (in terms of muckpile size distribution).' It is postulated there are no logical reasons (besides the current lack of means to infer rock mass properties in the blind zones of the bench and onsite precedents) for drilling a regular blast pattern over a rock mass that is inherently heterogeneous. Real and theoretical examples of such a method are presented.

Critical comparison of Julius Kruttschnitt Mineral Research Centre (JKMRC) blast fragmentation models

Blast fragmentation can have a significant impact on the profitability of a mine. An optimum run of mine (ROM) size distribution is required to maximise the performance of downstream processes. If this fragmentation size distribution can be modelled and controlled, the operation will have made a significant advancement towards improving its performance. Blast fragmentation modelling is an important step in Mine to Mill™ optimisation. It allows the estimation of blast fragmentation distributions for a number of different rock mass, blast geometry, and explosive parameters. These distributions can then be modelled in downstream mining and milling processes to determine the optimum blast design. When a blast hole is detonated rock breakage occurs in two different stress regions - compressive and tensile. In the-first region, compressive stress waves form a 'crushed zone' directly adjacent to the blast hole. The second region, termed the 'cracked zone', occurs outside the crush one. The widely used Kuz-Ram model does not recognise these two blast regions. In the Kuz-Ram model the mean fragment size from the blast is approximated and is then used to estimate the remaining size distribution. Experience has shown that this model predicts the coarse end reasonably accurately, but it can significantly underestimate the amount of fines generated. As part of the Australian Mineral Industries Research Association (AMIRA) P483A Mine to Mill™ project, the Two-Component Model (TCM) and Crush Zone Model (CZM), developed by the Julius Kruttschnitt Mineral Research Centre (JKMRC), were compared and evaluated to measured ROM fragmentation distributions. An important criteria for this comparison was the variation of model results from measured ROM in the-fine to intermediate section (1-100 mm) of the fragmentation curve. This region of the distribution is important for Mine to Mill™ optimisation. The comparison of modelled and Split ROM fragmentation distributions has been conducted in harder ores (UCS greater than 80 MPa). Further work involves modelling softer ores. The comparisons will be continued with future site surveys to increase confidence in the comparison of the CZM and TCM to Split results. Stochastic fragmentation modelling will then be conducted to take into account variation of input parameters. A window of possible fragmentation distributions can be compared to those obtained by Split . Following this work, an improved fragmentation model will be developed in response to these findings.

Stratigraphy, facies architecture and tectonic implications of the Upper Devonian to Lower Carboniferous Campwyn Volcanics of the northern New England Fold Belt

Upper Devonian to Lower Carboniferous strata of the Campwyn Volcanics of east central Queensland preserve a substantial sequence of first-cycle volcaniclastic sedimentary and coeval volcanic rocks that record prolonged volcanic activity along the northern New England Fold Belt. The style and scale of volcanism varied with time, producing an Upper Devonian sequence of mafic volcano-sedimentary rocks overlain by a rhyolitic ignimbrite-dominated sequence that passes upward into a Lower Carboniferous limestone-bearing sedimentary sequence. We define two facies associations for the Campwyn Volcanics. A lower facies association is dominated by mafic volcanic-derived sedimentary breccias with subordinate primary mafic volcanic rocks comprising predominantly hyaloclastite and peperite. Sedimentary breccias record episodic and high energy, subaqueous depositional events with clastic material sourced from a mafic lava-dominated terrain. Some breccias contain a high proportion of attenuated dense, glassy mafic juvenile clasts, suggesting a syn-eruptive origin. The lower facies association coarsens upwards from a lithic sand-dominated sequence through a thick interval of pebble- to boulder-grade polymict volcaniclastic breccias, culminating in facies that demonstrate subaerial exposure. The silicic upper facies association marks a significant change in eruptive style, magma composition and the nature of eruptive sources, as well as the widespread development of subaerial depositional conditions. Crystal-rich, high-grade, low- to high-silica rhyolite ignimbrites dominate the base of this facies association. Biostratigraphic age controls indicate that the ignimbrite-bearing sequences are Famennian to lower-mid Tournaisian in age. The ignimbrites represent extra-caldera facies with individual units up to 40 m thick and mostly lacking coarse lithic breccias. Thick deposits of pyroclastic material interbedded with fine-grained siliceous sandstone and mudstone (locally radiolarian-bearing) were deposited from pyroclastic flows that crossed palaeoshorelines or represent syn-eruptive, resedimented pyroclastic material. Some block-bearing lithic-pumice-crystal breccias may also reflect more proximal subaqueous silicic explosive eruptions. Crystal-lithic sandstones interbedded with, and overlying the ignimbrites, contain abundant detrital volcanic quartz and feldspar derived from the pyroclastic deposits. Limestone is common in the upper part of the upper facies association, and several beds are oolitic (cf. Rockhampton Group of the Yarrol terrane). Overall, the upper facies association fines upward and is transgressive, recording a return to shallow-marine conditions. Palaeocurrent data from all stratigraphic levels in the Campwyn Volcanics indicate that the regional sediment-dispersal direction was to the northwest, and opposed to the generally accepted notion of easterly sediment dispersal from a volcanic arc source. The silicic upper facies association correlates in age and lithology to Early Carboniferous silicic volcanism in the Drummond (Cycle 1) and Burdekin Basins, Connors Arch, and in the Yarrol terranes of eastern Queensland. The widespread development of silicic volcanism in the Early Carboniferous indicates that silicic (rift-related) magmatism was not restricted to the Drummond Basin, but was part of a more substantial silicic igneous province.

Stereological and other methods applied to rock joint size estimation - Does Crofton's theorem apply?

A number of authors concerned with the analysis of rock jointing have used the idea that the joint areal or diametral distribution can be linked to the trace length distribution through a theorem attributed to Crofton. This brief paper seeks to demonstrate why Crofton's theorem need not be used to link moments of the trace length distribution captured by scan line or areal mapping to the moments of the diametral distribution of joints represented as disks and that it is incorrect to do so. The valid relationships for areal or scan line mapping between all the moments of the trace length distribution and those of the joint size distribution for joints modeled as disks are recalled and compared with those that might be applied were Crofton's theorem assumed to apply. For areal mapping, the relationship is fortuitously correct but incorrect for scan line mapping.

Selective entrainment of sediment graded by size and density under waves

The influence of near-bed sorting processes on heavy mineral content in suspension is discussed. Sediment concentrations above a rippled bed of mixed quartz and heavy mineral sand were measured under regular nonbreaking waves in the laboratory. Using the traditional gradient diffusion process, settling velocity would be expected to strongly affect sediment distribution. This was not observed during present trials. In fact, the vertical gradients of time-averaged suspension concentrations were found to be similar for the light and heavy minerals, despite their different settling velocities. This behavior implies a convective rather than diffusive distribution mechanism. Between the nonmoving bed and the lowest suspension sampling point, fight and heavy mineral concentration differs by two orders of magnitude. This discrimination against the heavy minerals in the pickup process is due largely to selective entrainment at the ripple face. Bed-form dynamics and the nature of quartz suspension profiles are found to be little affected by the trialed proportion of overall heavy minerals in the bed (3.8-22.1%).

Pyramidal cell heterogeneity in the visual cortex of the nocturnal new world owl monkey (aotus trivirgatus)

Recent studies have revealed marked variation in pyramidal cell structure in the visual cortex of macaque and marmoset monkeys. In particular, there is a systematic increase in the size of, and number of spines in, the arbours of pyramidal cells with progression through occipitotemporal (OT) visual areas. In the present study we extend the basis for comparison by investigating pyramidal cell structure in visual areas of the nocturnal owl monkey. As in the diurnal macaque and marmoset monkeys, pyramidal cells became progressively larger and more spinous with anterior progression through OT visual areas. These data suggest that: 1. the trend for more complex pyramidal cells with anterior progression through OT visual areas is a fundamental organizational principle in primate cortex; 2. areal specialization of the pyramidal cell phenotype provides an anatomical substrate for the reconstruction of the visual scene in OT areas; 3. evolutionary specialization of different aspects of visual processing may determine the extent of interareal variation in the pyramidal cell phenotype in different species; and 4. pyramidal cell structure is not necessarily related to brain size. Crown Copyright (C) 2003 Published by Elsevier Science Ltd on behalf of IBRO. All rights reserved.

Poor correlation of mid-femoral measurements by CT and hip measurements by DXA in the elderly

Background and aims: Hip fracture is a devastating event in terms of outcome in the elderly, and the best predictor of hip fracture risk is hip bone density, usually measured by dual X-ray absorptiometry (DXA). However, bone density can also be ascertained from computerized tomography (CT) scans, and mid-thigh scans are frequently employed to assess the muscle and fat composition of the lower limb. Therefore, we examined if it was possible to predict hip bone density using mid-femoral bone density. Methods: Subjects were 803 ambulatory white and black women and men, aged 70-79 years, participating in the Health, Aging and Body Composition (Health ABC) Study. Bone mineral content (BMC, g) and volumetric bone mineral density (vBMD, mg/cm(3)) of the mid-femur were obtained by CT, whereas BMC and areal bone mineral density (aBMD, g/cm(2)) of the hip (femoral neck and trochanter) were derived from DXA. Results: In regression analyses stratified by race and sex, the coefficient of determination was low with mid-femoral BMC, explaining 6-27% of the variance in hip BMC, with a standard error of estimate (SEE) ranging from 16 to 22% of the mean. For mid-femur vBMD, the variance explained in hip aBMD was 2-17% with a SEE ranging from 15 to 18%. Adjusting aBMD to approximate volumetric density did not improve the relationships. In addition, the utility of fracture prediction was examined. Forty-eight subjects had one or more fractures (various sites) during a mean follow-up of 4.07 years. In logistic regression analysis, there was no association between mid-femoral vBMD and fracture (all fractures), whereas a 1 SD increase in hip BMD was associated with reduced odds for fracture of similar to60%. Conclusions: These results do not support the use of CT-derived mid-femoral vBMD or BMC to predict DXA-measured hip bone mineral status, irrespective of race or sex in older adults. Further, in contrast to femoral neck and trochanter BMD, mid-femur vBMD was not able to predict fracture (all fractures). (C) 2003, Editrice Kurtis.

Wetting response of KrF laser ablated polyimide surfaces

The wettability of polyimide surfaces microstructured using KrF laser radiation at fluences above the material ablation threshold was studied by static contact angle measurements. The laser-treated surfaces present a morphology consisting of conical features whose dimensions and areal density depend on the fluence. The effect of these parameters on the surface apparent contact angle depends on the wetting regime. When wetting occurs in the homogeneous regime, the apparent contact angle of the treated surfaces increases with the radiation fluence because the cone dimensions increase. In contrast, when wetting occurs in the heterogeneous regime, the apparent contact angle increases with the radiation fluence because the average distance between cones increases. The apparent water contact angle of the laser-treated surfaces can reach values as high as 162 degrees, as compared to 75 degrees for virgin polyimide.