The geology and genesis of massive sulphide, barite-gold deposits on Wetar Island, Indonesia

Volcanic hosted massive sulphide mounds are preserved at Wetar Island, Indonesia with flanking Au-Ag-Hg bearing baritic ore bodies.  Wetar Island measures 100 km x 40 km and is part of the Inner Banda Arc, formed during the arc-continent collision of the NNE moving Indian-Australian plate beneath the Eurasian plate.  The island is composed entirely of Oligocene to Recent volcanics and minor oceanic sediments with centres of mineralisation at Kali Kuning (KK3) and Lerokis that are located approximately 3 km inland at an elevation of 400-500 m.  The orebodies occur marginal to rhyodacite domes within hydrothermally altered calc-alkaline volcanics which overly ocean floor basaltic - andesites.  40Ar/39Ar dating of biotite grains from a syeno-granite intrusion from the Meron area yielded a Zanclian age of 4.72 ± 0.22 Ma, biotites from a post-mineralisation overlying dacitic flow yielded a Piacenzian age of 2.4 ± 0.28 Ma. The massive sulphides are dominantly pyrite with minor chalcopyrite in upper parts, the pyrite is arsenian (up to 6.7 wt% As) and cut by late fractures infilled with covellite, chalcocite, tennantite-tetrahedrite, enargite, bornite and Fe-poor sphalerite.  Mining removed the associated Au-Ag-bearing barite sands (2.17  Mt at 3.98 g/t Au at Lerokis; 1.9 Mt at 4.63 g/t Au at Kali Kuning), with the sulphide mounds at each deposit remaining unexploited.  The barite ores are generally friable and are cemented by a series of complex arsenates, sulphates with gold present as &lt; 10&mu;m free grains.  Anhedral &lt; 20&mu;m inclusions of sulphides and sulphosalts are present within the barite.  The morphology of the barite within the deposits ranges from euhedral rectangular, rhombohedral and polyhedral crystals up to 6 mm in diameter to finer subhedral to anhedral crystals towards the footwall and hanging wall of deposits.  Linear and pipe-like barite- Fe-oxide structures are evident and are fluid feeders for the barite ore bodies.</p

New information on Neoproterozoic-Cambrian geology and the Triassic unconformity around Groby, southern Charnwood Forest, UK

Detailed investigations utilizing borehole drilling, geophysical techniques and revision mapping have elucidated the geological evolution of southern Charnwood Forest. This study confirms that the South Charnwood Diorite was emplaced in latest Neoproterozoic times and has a broadly concordant intrusive contact with underlying volcaniclastic strata of the Charnian Supergroup. Following erosion that unroofed the diorite, an Early Cambrian marine transgression deposited an unconformable covering of Brand Group strata. In end-Silurian times, the region experienced orogenic compression and folding along a dominant NW–WNW tectonic grain. ‘Phase 1’ structures with these orientations include the Charnwood Anticline and a transecting, penetrative cleavage that is mainly developed in the stratiform Charnian rocks. Further manifestations of this deformation were systems of NW-trending faults, the most important of which is the Groby Reverse Fault. This complex structure is described here for the first time; it features a narrow tectonic slice of Brand Group rocks, which was thrown down into the South Charnwood Diorite. The courses of younger, ‘Phase 2’ faults are also revealed by the present study; they are orthogonal to, and thus offset the earlier NW structures. During Permian times, the area was stripped of its Carboniferous cover, resulting in a rugged pre-Triassic topography. This study has shown that the South Charnwood Diorite was eroded into low-lying, NW-elongated, steep-sided domes (bornhardts). It has also revealed the configuration of an associated palaeo-valley system, which suggests that regional tilting associated with development of the syn-Triassic Hinckley Basin to the south-west of Charnwood Forest may have influenced drainage directions before burial of the hill-range beneath desert sediments of the Mercia Mudstone Group

Subsurface absorption of anthropogenic warming of the land surface: The case of the world's largest brickworks (Stewartby, Bedfordshire, UK)

Stewartby works, for a time the world's largest brickworks, began operation around the start of the twentieth century and closed in 2008. Subsurface temperature measurements are available in its vicinity, obtained as part of monitoring of an adjacent landfill in one of the former quarries for the Oxford Clay, which was the raw material for brick manufacture. A striking subsurface temperature anomaly, an increment of ~ 12 °C, was first measured in 2004, and has subsequently decayed over time. The anomaly is centred beneath one of the former brick kilns, which operated between 1935 and 1991. To investigate processes of heat absorption by the shallow subsurface, this anomaly has been modelled as a consequence of conductive heat flow into the ground due to the operation of the ~ 3000 m&lt;sup&gt;2&lt;/sup&gt; kiln. This modelling indicates that a very large amount of heat energy was transported into the subsurface; we estimate the typical downward surface heat flow during operation of the kiln as ~ 1 W m &lt;sup&gt;−2&lt;/sup&gt; and the energy stored in the subsurface beneath it at its time of shutdown as ~ 6 TJ, or ~ 0.03% of that released by the fuel for heating the kiln, such that the total heat energy stored beneath this multi-kiln site peaked at ~ 200 TJ. The proportion of heat energy transported into the subsurface was relatively low due to the nature of the Oxford Clay, which has a low thermal conductivity (~ 0.8 W m &lt;sup&gt;−1&lt;/sup&gt; °C &lt;sup&gt;−1&lt;/sup&gt;) and diffusivity (~ 0.3 mm&lt;sup&gt;2&lt;/sup&gt; s &lt;sup&gt;−1&lt;/sup&gt;); in a more conductive lithology it might well have been three times greater. After kiln shutdown this subsurface thermal anomaly began to dissipate by upward heat conduction and release of heat into the atmosphere; at present about half of the peak energy stored remains, decreasing at ~ 1% per year, the maximum temperature anomaly being currently ~ 7 °C at a depth of ~ 30 m and the typical upward heat flow during this span of time having exceeded the regional ~ 40 mW m&lt;sup&gt;− 2&lt;/sup&gt; background by roughly an order of magnitude. We believe this to be the first documented case whereby a subsurface thermal anomaly associated with operation of industrial plant has been related in detail to the history of site operations. This case study thus bears upon the controversial topic of the development of subsurface heat islands in general, and the associated perturbation of the thermal state of the subsurface as a result of anthropogenic warming of the atmosphere. It has previously been suggested that the worldwide heat gain in the subsurface over recent decades has exceeded that in the atmosphere by a factor of three. We show that this result is subject to some uncertainty, for example because it does not factor in lateral variations in thermal properties. Nonetheless, our case study demonstrates dissipation of a subsurface thermal anomaly by heat transport into the atmosphere. This indicates that warming of the atmosphere will be sustained in the future by dissipation of the large amount of energy stored in pre-existing subsurface thermal anomalies on a global scale, an issue of major societal implications that demands more detailed investigation

Temporal association of arc–continent collision, progressive magma contamination in arc volcanism and formation of gold-rich massive sulphide deposits on Wetar Island (Banda arc)

Whole-rock 87Sr/86Sr and ?18O analyses of volcanic rocks and 3He/4He analyses of sulphides and sulphates from mineralized rocks on Wetar, Indonesia indicate a variable contribution of assimilated crustal material or sediment sourced from the subducted Australian craton to the south. These new data support the idea of progressive source contamination with precisely dated events showing that Wetar Island hosts the most extreme examples of crustal assimilation in the region. The increased continental contamination occurs during the Pliocene (Zanclian to Piacenzian) during distinct magmatic events between 5 and 4 Ma, and at 2.4 Ma when 87Sr/86Sr ratios in unaltered lavas, with whole-rock ?18O values between 5.7 and 9.6‰, increase from 0.707484 to extreme radiogenic values of 0.711656.The earlier of these magmatic events is important in the generation of the hydrothermal systems responsible for the mineralization recorded on Wetar. Samples from this yield radiogenic 3He/4He ratios between 0.5 and 1.4 R/RA, similar to the data from volcanic rocks on nearby Romang. The later magmatic event coincides with the arrival of the Australian Continental Margin at the subduction zone along the Banda arc. Progressive incorporation of continental-sourced components into the source region below the Wetar Island edifice coincides with the formation of gold-rich volcanogenic massive sulphide deposits hosted within the contaminated volcanic pile

Dynamic iris biometry: a technique for enhanced identification

<p>Abstract</p> <p>Background</p> <p>The iris as a unique identifier is predicated on the assumption that the iris image does not alter. This does not consider the fact that the iris changes in response to certain external factors including medication, disease, surgery as well as longer term ageing changes. It is also part of a dynamic optical system that alters with light level and focussing distance. A means of distinguishing the features that do not alter over time from those that do is needed. This paper applies iris recognition algorithms to a newly acquired database of 186 iris images from four subjects. These images have greater magnification and detail than iris images in existing databases. Iris segmentation methods are tested on the database. A new technique that enhances segmentation is presented and compared to two existing methods. These are also applied to test the effects of pupil dilation in the identification process.</p> <p>Findings</p> <p>Segmentation results from all the images showed that using the proposed algorithm accurately detected pupil boundaries for 96.2% respectively of the images, which was an increase of 88.7% over the most commonly used algorithm. For the images collected, the proposed technique also showed significant improvement in detection of the limbal boundary compared to the detection rates using existing methods. With regard to boundary displacement errors, only slight errors were found with the proposed technique compared to extreme errors made when existing techniques were applied. As the pupil becomes more dilated, the success of identification is increasingly more dependent on the decision criterion used.</p> <p>Conclusions</p> <p>The enhanced segmentation technique described in this paper performs with greater accuracy than existing methods for the higher quality images collected in this study. Implementation of the proposed segmentation enhancement significantly improves pupil boundary detection and therefore overall iris segmentation. Pupil dilation is an important aspect of iris identification; with increasing dilation, there is a greater risk of identification failure. Choice of decision criterion for identification should be carefully reviewed. It needs to be recognised that differences in the quality of images in different databases may result in variations in the performance of iris recognition algorithms.</p

The development of volcanic hosted massive sulfide and barite–gold orebodies on Wetar Island, Indonesia

Wetar Island is composed of Neogene volcanic rocks and minor oceanic sediments and forms part of the Inner Banda Arc. The island preserves precious metal-rich volcanogenic massive sulfide and barite deposits, which produced approximately 17 metric tonnes of gold. The polymetallic massive sulfides are dominantly pyrite (locally arsenian), with minor chalcopyrite which are cut by late fractures infilled with covellite, chalcocite, tennantite–tetrahedrite, enargite, bornite and Fe-poor sphalerite. Barite orebodies are developed on the flanks and locally overly the massive sulfides. These orebodies comprise friable barite and minor sulfides, cemented by a series of complex arsenates, oxides, hydroxides and sulfate, with gold present as &lt;10 lm free grains. Linear and pipe-like structures comprising barite and ironoxides beneath the barite deposits are interpreted as feeder structures to the barite mineralization. Hydrothermal alteration around the orebodies is zoned and dominated by illite–kaolinite–smectite assemblages; however, local alunite and pyrophyllite are indicative of late acidic, oxidizing hydrothermal fluids proximal to mineralization. Altered footwall volcanic rocks give an illite K–Ar age of 4.7±0.16 Ma and a 40Ar/39Ar age of 4.93±0.21 Ma. Fluid inclusion data suggest that hydrothermal fluid temperatures were around 250–270C, showed no evidence of boiling, with a mean salinity of 3.2 wt% equivalent NaCl. The d34S composition of sulfides ranges between +3.3&amp; and +11.7&amp; and suggests a significant contribution of sulfur from the underlying volcanic edifice. The d34S barite data vary between +22.4&amp; and +31.0&amp;, close to Miocene seawater sulfate. Whole rock 87Sr/86Sr analyses of unaltered volcanic rocks (0.70748–0.71106) reflect contributions from subducted continental material in their source region. The 87Sr/86Sr barite data (0.7076–0.7088) indicate a dominant Miocene seawater component to the hydrothermal system. The mineral deposits formed on the flanks of a volcanic edifice at depths of ~2 km. Spectacular sulfide mounds showing talus textures are localized onto faults, which provided the main pathways for high-temperature hydrothermal fluids and the development of associated stockworks. The orebodies were covered and preserved by post-mineralization chert, gypsum, Globigerina-bearing limestone, lahars, subaqueous debris flows and pyroclastics rocks