Formation and evolution of the chromitites of the Stillwater Complex : a trace element study

Large layered intrusions, such as the Stillwater Complex, contain cyclic units of chromite-rich layers (cm to m thick) having kilometre-scale lateral extension. Chromite cumulates are among the first to form after new primitive melt injections into the magma chamber. Therefore, chromite cumulates could be used to investigate the nature of the parental magma, given the fact that chromite preserves its primary original magmatic composition. The cooling and crystallization history of large layered intrusions is long, complex, and involves multiple injections of hot primitive magma into an evolving and fractionating magma chamber. Our study on Stillwater chromites shows that the early crystallized chromite experiences various post-cumulus processes with the interstitial silicate melt, such as the precipitation of chromite overgrowths on early formed cumulus chromite and/or the reaction - reequilibration of early formed cumulus chromite. These processes have modifed the primary magmatic composition of the chromite making it difficult to identify the parental magma. Moreover, mineralogical evidence for chromite - interstitial melt interactions have probably been obliterated during late post-magmatic textural maturation and recrystallization which tends to homogenize chromite grain size and composition

The Origin of Xenoliths with Cumulus Textures Found Above the Subsurface Extension of the Stillwater Complex, Montana

The Archean Stillwater Complex is a large layered mafic-ultramafic intrusion (LMI) exposed in the Beartooth Mountains of south-central Montana. Gravity measurements suggest that the north-dipping complex extends under cover at depth. Some of the exposures located above the subsurface Stillwater Complex are younger Cretaceous stocks (Susie Peak and Sliderock Mountain stocks), diorite sills and andesite dikes, exposed north of the complex, passed through area of the gravity anomaly that may be the Stillwater Complex. In the summer of 2013, samples of the stocks and their included xenoliths (foreign rock fragments; commonly metamorphosed to greenschist facies conditions) were collected for study. Xenoliths with textures reminiscent of Stillwater Complex cumulates were chosen for further investigation. The host andesitic rocks containing the xenoliths exhibit porphyritic textures—phenocrysts of plagioclase, amphibole ± biotite occur in a finer-grained groundmass of the same minerals. Electron microprobe analyses of amphibole grains from both the host and xenolith are comparable in composition. Electron microprobe analyses for two samples of coexisting xenolith amphibole (Tschermakitic hornblende, magnesio-hastingsite) and plagioclase (rim An83-91Ab17-9) constrain temperature conditions at various pressures (P at 3, 5, and 6 kb; T = 500-656°C, respectively using Holland and Blundy (1994). These conditions are consistent with amphibolite facies metamorphism. Few xenoliths retain the original igneous mineralogy (with the exception of plagioclase) but one sample contains relict “Stillwater-like” mineralogy (e.g., clinopyroxene) and another contains chromite. Plagioclase and relict clinopyroxene compositions are somewhat comparable to Stillwater mineral compositions. The fact that the xenoliths are now metamorphosed and highly altered suggests that either they were metamorphosed prior to their inclusion in the melt or were metamorphosed or hydrothermally altered as a result of incorporation into the melt

System and method for improved rotor tip performance

Embodiments of systems and methods for enhancing the performance of rotary wing aircraft through reduced torque, noise and vibration are disclosed. In one embodiment, a method includes configuring the rotorcraft in a selected flight condition, communicating input signals to a control system operable to position sails coupled to tips of blades of a rotor assembly, processing the input signals according to a constraint condition to generate sail positional information, and transferring the sail positional information to the sail. Alternately, input signals may be communicated to a control system operable to position a plurality of sails, each sail having an aerodynamic shape and positioned proximate to a tip portion of the rotor blade. The input signals may be configured to rotate each sail about a longitudinal axis into a corresponding pitch angle independently of the other sails

System and method for improved rotor tip performance

The present invention discloses systems and methods for the performance enhancement of rotary wing aircraft through reduced torque, noise and vibration. In one embodiment, a system includes a sail having an aerodynamic shape positioned proximate to a tip of the rotor blade. An actuator may be configured to rotate the sail relative to the blade tip. a A control system receives information from a rotorcraft system and commands the actuator to rotate the sail to a predetermined favorable rotor blade operating condition. In another embodiment, a method includes configuring the rotorcraft in a selected flight condition, communicating input signals to a control system operable to position sails coupled to tips of blades of a rotor assembly, processing the input signals according to a constraint condition to generate sail positional information, and transferring the sail positional information to the sail

Processes leading to concentration of platinum-group elements in chromite rich rocks

Platinum-group elements are enriched in the ultramafic parts of the Stillwater, Bushveld and Great Dyke Complexes. Processes whereby this enrichment may occur are considered

FPGA-Based Tracklet Approach to Level-1 Track Finding at CMS for the HL-LHC

During the High Luminosity LHC, the CMS detector will need charged particle tracking at the hardware trigger level to maintain a manageable trigger rate and achieve its physics goals. The tracklet approach is a track-finding algorithm based on a road-search algorithm that has been implemented on commercially available FPGA technology. The tracklet algorithm has achieved high performance in track-finding and completes tracking within 3.4 $\mu$s on a Xilinx Virtex-7 FPGA. An overview of the algorithm and its implementation on an FPGA is given, results are shown from a demonstrator test stand and system performance studies are presented.Comment: Submitted to proceedings of Connecting The Dots/Intelligent Trackers 2017, Orsay, Franc

MAPS, SECTIONS, AND STRUCTURE-CONTOUR DIAGRAMS SHOWING THE GEOLOGY AND GEOCHEMISTRY OF THE MOUAT NICKEL-COFFER PROSPECT, STILLWATER COMPLEX, STILLWATER COUNTY, MONTANA

ABSTRACT Deposits of magmatic nickel-copper (Ni-Cu) sulfides are concentrated near the base of the Stillwater Complex, a Late Archean mafic to ultramafic layered intrusion exposed on the north edge of the Beartooth Mountains, Montana. Extensive drilling and limited underground development work by the Anaconda Minerals Company has delineated the sub-surface extent of one of these deposits, the Mouat Ni-Cu prospect or deposit. Structural interpretation shows that rocks of the Mountain View area of the Stillwater Complex are folded into a broad syncline which is inclined and cut by several generations of faults. The oldest faults strike northeast and have near vertical dips. These faults are cut by northweststriking, near vertical faults showing left-lateral separation. Apparent separation on these faults are less than 500 ft. Two high-angle reverse faults, the Lake fault and the Bluebird thrust, truncate the Mouat deposit on the northeast and the southwest, respectively. Sulfide minerals that constitute this deposit are concentrated at the lower contact of the Stillwater Complex within the Basal series and within and adjacent to very discontinuous, irregularly shaped Stillwater-associated sills and dikes that intrude the metasedimentary rocks underlying the complex. The base of the Stillwater Complex shows considerable relief over short distances; as a result, the thickness of the Basal series ranges from 0 to 450 ft. However, there is no clear evidence that sulfides at the base of the complex pooled in depressions on the floor of the complex. Intensity of faulting and the discontinuous nature of the matrix-to-massive sulfide mineralization do not allow probabilistic tonnage and grade estimates to be made despite the density of drilling

An overview of the design, construction and performance of large area triple-GEM prototypes for future upgrades of the CMS forward muon system

GEM detectors are used in high energy physics experiments given their good spatial resolution, high rate capability and radiation hardness. An international collaboration is investigating the possibility of covering the 1.6 < vertical bar eta vertical bar < 2.4 region of the CMS muon endcaps with large-area triple-GEM detectors. The CMS high-eta area is actually not fully instrumented, only Cathode Strip Chamber (CSC) are installed. The vacant area presents an opportunity for a detector technology able to to cope with the harsh radiation environment; these micropattern gas detectors are an appealing option to simultaneously enhance muon tracking and triggering capabilities in a future upgrade of the CMS detector. A general overview of this feasibility study is presented. Design and construction of small (10cm x 10cm) and full-size trapezoidal (1m x 0.5m) triple-GEM prototypes is described. Results from measurements with x-rays and from test beam campaigns at the CERN SPS is shown for the small and large prototypes. Preliminary simulation studies on the expected muon reconstruction and trigger performances of this proposed upgraded muon system are reported