Interpretation of geophysical data obtained near Lumberton, North Carolina suggests the presence of a granitic pluton buried beneath Slate Belt-like rocks. A 239 m drill core retrieved from a hole 7.5 km southeast of the city of Lumberton consists of interlayered felsic and mafic volcanics of lower amphibolite grade metamorphism. Dipping reflections in a nearby 16. 5 km long seismic reflection line are believed to be from these volcanics, which are interpreted to be 3.5 km or more in thickness. Below these volcanics is an acoustically transparent zone which is interpreted to be caused by a granitic pluton. This hypothesis is supported by gravity data, which show a -35 mgal Bouguer gravity anomaly, and the relatively high heat flow of 63.4±5 mW/m² obtained in the drill hole, both of which are characteristic of Hercynian granitic plutons in the southeastern United States. Gravity modeling suggests that the body is nearly circular in shape, about 45 km in diameter, and nearly 14 km in thickness. Deep, nearly horizontal reflections in the 5 to 7 sec time range are interpreted to be from the base of the granitoid at a depth of about 17 km. One possible explanation for these reflections is that the granitoid is allochthonous; emplaced elsewhere and then transported to its present position along a sole thrust. The high heat flow suggests that the body is unmetamorphosed and the thrusting, which may post-date or be coeval with the intrusion, would thus be late Paleozoic in age. / M.S.

M.S.

The Clarno Formation is a series of volcanic, volcaniclastic, and related intrusive rocks located in central Oregon. It is the westernmost extent of a broader Eocene magmatic belt that covers much the western United States. The magmatic belt stretches eastward from Oregon to western South Dakota, and from the Canadian Yukon to northern Nevada. While once attributed to subduction of the Farallon Plate under North America, more recent work suggests that a more complex tectonic regime involving extension was in place during the early Cenozoic. In the vicinity of Mitchell, Oregon, the Clarno Formation is well represented along with Mesozoic metamorphic and sedimentary units, and younger Tertiary volcanic and volcaniclastic units. In this area, Clarno volcanic activity occurred from ~52-42 Ma, producing mostly andesites and related volcaniclastic rocks. The Mitchell area is also underlain by related intrusive bodies ranging from basalt to rhyolite in composition. The Clarno was most active at ~49 Ma, and is dominantly calcalkaline. In addition, there are several coeval alkaline and peraluminous intrusives also scattered throughout the Clamo Formation. While these suites are less voluminous than the calc-alkaline magmatism, they offer insight into the tectonic and magmatic processes at work in this area during the Eocene. Whereas silicic intrusions are common in the Clarno, the high-silica rhyolite dike on the south face of Scott Butte is unusual due to its large garnet phenocrysts. The existence of primary garnet in rhyolitic magmas precludes middle to upper crustal genesis, a common source for silicic magmas. ⁴⁰Ar/³⁹Ar age determinations of the biotite indicate an age of ~51 Ma. This is after andesitic volcanism had commenced, but prior to the most active period of extrusion. The presence of the almandine garnet indicates that the dike represents partial melting of lower crustal (18-25 km) material. The presence of a high field strength element (HFSE) depletion commonly associated with subduction are magmatism indicates that either the source material had previously been metasomatised, or that some subduction melts/fluids (heat source) mixed with the crustal melt. Two alkaline suites, a high-K calc-alkaline basanite (Marshall and Corporate Buttes) and alkaline minette/kersantite lamprophyres (near Black Butte and Mud Creek), were emplaced ~49 Ma, during the height of calc-alkaline activity. The basanite lacks the HFSE depletion common in the other Clarno rocks. Instead it has a HIMU-type (eg. St Helena) ocean island basalt affinity, resulting from partial melting of enriched asthenospheric mantle. In contrast, the lamprophyres represent hydrous partial melts of metasomatized litho spheric mantle veins and bodies. Alkaline magmatism was not limited to the most active periods of calc-alkaline activity. The emplacement of an alkali basalt (Hudspeth Mill intrusion) at ~45 Ma occurred four million years after the largest pulse of volcanism, but still during calcalkaline activity. This alkali basalt represents partial melting of metasomatized lithospheric mantle. The occurrence of these alkaline suites coeval with the calc-alkaline activity is significant in that it disputes prior subduction theories for the broader Eocene magmatism that are based on spatial and temporal variations from calc-alkaline to alkaline magmatism. These suites also give further insight into the complex tectonic regime that existed in Oregon during the Eocene. The occurrence of asthenospheric melts not caused by fluid fluxing, along with lower lithospheric alkaline melts, are normally associated with extension. Extension provides these magmas with both the mechanism for melting, and the ability to reach shallow crust with little or no contamination. Extension is in agreement with both White and Robinson's (1992) interpretation that most Clarno Formation deposition occurred in extensional basins, and with other provinces in the broader Eocene magmatic belt. / Graduation date: 2002

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

Thesis submitted for the degree MAGISTER SCIENTIAE to the Faculty of Science, Department of Geology, University of the Witwatersrand, Johannesburg / The Koperberg Suite intrusion at Jubilee, Namaqualand varies in composition from anorthosite, through mica diorite to pyroxene leucodiorite and pyroxene diorite. Detailed mapping and petrological studies of these rocks indicate that they were sequentially emplaced into the Concordia Granite country rocks, and that each of the rock types represent discrete magmatic events. The sequence of intrusion is from more acidic to more basic. Whole-rock geochemical analyses indicate that these rocks represent cumulates involving variable proportions of plagioclase, orthopyroxene, mica, quartz, oxides and immiscible sulphides. These cumulate phases intruded into the Concordia Granite at the time of peak of metamorphism and deformation in the Okiep Copper District, i.e, about 1030Ma ago, At the time of intrusion, the country rocks were under going partial melting under high grade (granulite facies) metamorphic conditions. and granitic anatects were present in the crust. Hybridisation of basic magma and granitic melts occurred within the shear zones along which the basic magmas ascended. The En content of orthopyroxene in the Koperberg Suite exceeds the An content of plagioclase. This is atypical of basic intrusions and is a consequence of this mixing. Mixing calculations based on the initial 87Sr/86Srratio (Ru) of the Jubilee samples at 1030Ma, imply high levels of assimilation (as much as 80% assimilation in the case of anorthositic rocks) between a granitic component, similar in composition to the Nababeep Gneiss and a mantle-derived basic magma. Sulphide mineralisation was initiated by the assimilation process, which caused the separation of immiscible sulphides from the hybridised magma. Subsequent oxidation of the original sulphide assemblage produced bornite, chalcopyrite and Ti-poor magnetite. / Andrew Chakane 2019

Oxidized hydrous intermediate composition magmas are responsible for porphyry copper (Cu ±Mo ±Au) deposits and epithermal Au ore deposits formed globally in the shallow crust (Sillitoe, 2010; Seedorff et al., 2005). Recently, zircon geochemistry has been used to characterize both productive and barren intrusions associated with porphyry Cu-Au ore deposits. Zircon composition differs slightly between the two intrusive groups, and researchers have proposed that zircon in productive intrusions has crystallized from a relatively more oxidized melt compared to barren intrusions (Ballard et al., 2002; Muñoz et al., 2012). Zircon rare earth elements record anomalies in Ce and Eu contents that allow estimation of the ratio of oxidized versus reduced species, i.e. Ce⁴⁺/Ce³⁺ (Ce[superscript IV]/Ce[superscript III]) and Eu³⁺/Eu²⁺ (Eu/Eu*)[subscript CN]. This study focuses on understanding the compositions of Eocene magmas associated with sediment hosted Carlin gold deposits and the gold-copper ores of the Battle Mountain porphyry Cu-Au-skarn district in northern Nevada. Zircon trace element composition was analyzed using LA-ICP-MS and SHRIMP-RG to determine differences between mineralizing and non-mineralizing intrusions in northern Nevada and to compare these compositions with known porphyry Cu-Au type magmas. These zircon and rock compositional data was then used to test the hypothesis of a magmatic origin of the Carlin type gold deposits (Muntean et al., 2011). Zircon U-Pb ages were calculated using multiple SHRIMP-RG spot analyses of each sample for two Carlin biotite porphyry dikes, two Battle Mountain porphyry dikes and the granodiorite of the Copper Canyon stock. The new U-Pb age dates for Carlin porphyry dikes are 38.7 ± 0.5 Ma and 38.8 ± 0.4 Ma. The age of the Copper Canyon stock is 38.0 ± 0.7 Ma, and the age of the Battle Mountain porphyry dikes are 40.2 ± 0.4 Ma and 41.3 ± 0.4 Ma. The Carlin dike ages are the same age, within uncertainty, with previous studies conducted (Mortensesn et al., 2000). The productive porphyry dikes from the Battle Mountain district have Ce(IV)/Ce(III) ratios of 500 to 10000 and a wide range of (Eu/Eu*)[subscript CN] values between 0.3 and 0.7 respectively. Carlin porphyry dikes have Ce(IV)/Ce(III) values between 100 and 1000, and a more limited (Eu/Eu*)[subscript CN] range of 0.5 to 0.7. Barren Eocene intrusions at Harrison Pass and Caetano have much lower Ce(IV)/Ce(III) ratios that range from 20 to 500, and have a very large span of (Eu/Eu*)[subscript CN] from 0.03 to 0.6. Calculated Ce(IV)/Ce(III) and (Eu/Eu*)[subscript CN] of zircon of this study illustrate a distinction between productive and barren intrusions in northern Nevada, and demonstrate a geochemical link between porphyry type magmas and dikes associated with Carlin type gold deposits. These ratios may provide a useful means of evaluating potentially economic geologic terranes and serving as a method to infer relative oxidation state of zircon bearing intrusive rocks. / Graduation date: 2013

Thesis (M.S.)--Indiana University, 2009. / Title from screen (viewed on February 2, 2010). Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Andrew P. Barth, Gabriel M. Filippelli, Kathy Licht. Includes vitae. Includes bibliographical references (leaves 102-110).

The Central Asia Orogenic Belt is one of the largest accretionary orogenic belts in the world. In this belt, many sulfide‐bearing mafic‐ultramafic intrusions occur along faults, including the Kalatongke complex in southeast Chinese Altay and the Huangshandong intrusion in east Tianshan. The Kalatongke complex is a composite body including ~308Ma dioritic intrusion and 287Ma sulfide‐bearing mafic intrusion. The dioritic intrusion consists of biotite‐hornblende gabbro, diorite and quartz diorite. This intrusion was formed from a mixture of an evolved mantle‐derived magma and a crust‐derived adakitic magma combined with fractional crystallization of clinopyroxene, amphibole and plagioclase. The mafic intrusion is dominantly made up of norite in which sulfide ores, including disseminated, massive Ni‐Cu and massive Cu‐rich ores, are hosted. This intrusion was formed from two different pulses of basaltic magmas that had different magma evolution histories. The early magma pulse reached sulfide‐saturation due to minor crustal contamination and a small amount of sulfide (<0.03%) was removed before the emplacement. The evolved magmas then entered a shallow magma chamber and assimilated crustal materials to attain sulfide‐saturation again. Sulfide liquids segregated from the magma to form massive Ni‐Cu and massive Cu‐rich ores through further fractionation and residual silicate melts formed norites. A second pulse of magma underwent removal of <0.02% sulfides with stronger crustal contamination, and re‐attained S‐saturation during the emplacement and became a phenocryst‐laden magma. This magma then intruded the earlier formed massive sulfide ores and norites, forming the disseminated sulfide ores. The Permian Huangshandong mafic‐ultramafic intrusion hosts the largest magmatic sulfide deposit in east Tianshan. It consists of a layered unit of lherzolite, gabbro and diorite and a massive unit of olivine gabbronorite and gabbronorite. Both units formed from siliceous high magnesium basaltic (SHMB) magmas derived from a hydrous, depleted mantle source. The two units of the Huangshandong intrusion formed from magmas that have undergone different processes through the evolution of the magma plumbing system. The early magma pulse gained sulfur‐saturation before the emplacement and small amounts of sulfide (<0.03%) were removed to result in a PGE‐depleted, high‐Mg magma. This magma achieved sulfide‐saturation again in a staging magma chamber through crustal contamination and fractional crystallization of olivine and Cr‐spinel (an AFC process) to form the layered unit. A second magma pulse underwent fractionation of more olivine +/‐ Cr‐spinel but less sulfide (<0.003%) removal before the emplacement and became evolved, PEG‐undepleted and low‐Mg before the injection into the magma chamber. Mixing of the two magmas triggered sulfide‐saturation to form sulfide ores with variable PGE, Ni and Cu compositions. The study suggests that SHMB‐like magmatism, produced by melting of depleted and hydrous mantle source, may be an important feature of orogenic belts. Mafic‐ultramafic intrusions formed from SHMB‐like magmas may host economic sulfide deposits, particularly sulfide Ni‐Cu sulfide deposits. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

No abstract available. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2013.

The Panzhihua intrusion is one of several large Fe-Ti oxide ore bearing intrusions related to the major flood volcanism of the Emeishan Large Igneous Province (ELIP), SW China. The Panzhihua intrusion in particular has recently become the focus of numerous studies owing to the excellent exposure in large open pit mining operations. The formation of Fe-Ti oxide ore layers has been the focus of these studies and has become a somewhat controversial topic with three separate models currently proposed for ore formation. The gabbroic Panzhihua intrusion extends for ± 19 km along strike, has a maximum thickness of 3000 m and hosts extensive (up to 60 m thick) Fe-Ti oxide ore layers in the lower portions of the intrusion. The intrusion has been divided into five zones: marginal zone (MGZ), lower zone (LZ), middle zone A (MZa), middle zone b (MZb) and the upper zone (UZ). The gabbroic rocks are comprised of plagioclase, clinopyroxene and interstitial Fe-Ti oxides with minor olivine. Apatite is present within the MZb only and shows no correlation with Fe-Ti oxide ore layers. Fe-Ti oxides are present throughout the stratigraphy of the intrusion. This is unlike typical layered intrusions where significant Fe-enrichment through fractionation of Fe-poor silicate phases (i.e. plagioclase) is required before Fe-Ti oxide saturation. There are no oxide-free cumulate rocks at the Panzhihua intrusion, implying either an evolved parent magma or very high Fe content of the source rocks. I present here new mineral composition data, whole-rock major and trace element geochemistry along with whole-rock Sr-Nd isotopes and PGEs in order to constrain the evolution of the Panzhihua parent magma en route from source to chamber and the formation of Fe-Ti oxide ore layers. Furthermore an initial pilot study using O-isotope data is conducted on Ti-magnetite and plagioclase separates from gabbroic vs. ore rocks. Results are coupled with detailed thermodynamic modeling using the software PELE in order to further constrain Fe-Ti oxide ore layer formation. The intrusion is characterised by extreme depletion of PGEs relative to the coeval flood basalts and picrites. High Cu/Pd and Pd/Pt imply two separate stages of S-saturated and S-undersaturated depletion of PGEs. Pd is highly compatible in sulphide and is quickly scavenged by sulphide liquids resulting in an increase in Cu/Pd of the residual liquid. Furthermore decoupling of Pd and Pt can be achieved by either late stage hydrothermal alteration or through S-undersaturated stage of PGE depletion where Pt is scavenged by Pt-rich alloys or oxide minerals. I show that the latter is more likely. Fractionation modeling suggests that the Panzhihua parent magma formed at depth from original picritic magma. This is consistent with several other recent studies on other layered intrusions of the ELIP. Sr-Nd isotopic ratios indicate very little crustal contamination has occurred en route to the current chamber. Sr and Nd concentrations of footwall rocks are too low to produce any significant change in initial Sr and Nd isotopic ratios of the intruding basaltic magmas, indicating that crustal contamination will not be indicated by Sr-Nd isotopic ratios. Gradational change in the Sr-Nd isotope ratios across the MGZ provides strong evidence for formation in an open system by multiple replenishments of progressively less contaminated magmas from depth. Contamination is difficult to constrain but must be occurring prior to emplacement at the current level (low Sr and Nd contents of footwall). A gradational upward decrease in highly incompatible element across the MGZ can then be explained by continuous magma flow, which effectively removes the evolved intercumulus liquids from the growing cumulate pile at the base of the chamber. The initial stages of formation of the Panzhihua intrusion are interpreted to result from prolonged low volume pulses of magma into a slowly opening chamber. The timing of Fe-Ti oxide crystallisation is fundamental in the understanding of the petrogenesis of ore layers. Distinct geochemical variation in whole-rock Fe2O3/TiO2 and Zr/Nb indicates that Timagnetite is the dominant oxide within the lower ± 270 m of the intrusion whereas above this level both Ti-magnetite and ilmenite are present as cumulus phases. This is interpreted to indicate a variation in the fO2 where the lower intrusion crystallises at higher fO2 relative to that above this level. Silicates within the ore layers, in particular plagioclase, are highly embayed and resorped where in contact with Fe-Ti oxides. This characteristic of the silicate grains implies early crystallisation prior to Fe-Ti oxides with subsequent disequilibrium conditions resulting in resorption. Furthermore distinct reaction rims of kaersutite amphibole, Fo-enriched olivine, An-enriched plagioclase and pleonaste are observed. The abundance of amphibole suggests H2O involvement in this reaction and consumption of silicates. A model for parent magma crystallisation at various H2O contents indicates that plagioclase crystallisation temperature is very sensitive to H2O content of the parent magma. Plagioclase crystallises early for “dry” compositions but significantly later for “wet” compositions. Fe-Ti oxide ore layers are generally well layered, contain gabbroic xenoliths and are observed raversing/cross-cutting the cumulate stratigraphy. I present here a new model for ore layer formation in order to account for these distinct features of the ore layers. A model invoking multiple replenishments of magma with variable oxide microphenocryst content, H2O content and volume is proposed. Magma evolving in the plumbing system and fed to the Panzhihua chamber is variably enriched in H2O, which results in significantly different crystallisation paths. High H2O magmas (> 2 wt %) crystallise Fe-Ti oxides early whereas low H2O magmas (< 1 wt %) crystallise oxides late. Early pulses of H2O-poor magma crystallise a sequence of plag+cpx+Fe-Ti oxide (±ol). Later pulses of H2Orich magma subsequently intrude the partially crystallised cumulate sequence incorporating and consuming previously crystallised silicates with subsequent early crystallisation of Ti-magnetite and formation of ore layers. H2O-rich magmas likely have suspended Ti-magnetite microphenocrysts as well, which crystallise at depth in the plumbing system. This model can account for the various characteristic features of the Fe-Ti oxide ore layers at the Panzhihua intrusion as well as other Fe-Ti oxide ore bearing intrusions in the region.