Mineralogical and Geochemical Characteristics Of Sudbury Breccia Adjacent To Footwall Cu-Ni-PGE Sulfide Veins and Structures In the Creighton and Coleman Deposits
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Abstract The Sudbury Breccia is an impactite that formed in the target rocks of the 1850 +1.3/–2.4 Ma Sudbury impact structure in Ontario, Canada. The breccia is interpreted to have formed during crater excavation or modification at the time of the impact event. Copper-Nickel-Platinum Group Elements sulfide melts moved away from contact mineralization at the base of the melt sheet to form veins and stockworks in the footwall. The distribution of both Sudbury Breccia and the later sulfide melts is partially controlled by pre-existing weaknesses in the footwall, such as lithological contacts; as a result, the two are often spatially associated. A combination of early magmatic-hydrothermal and late metamorphic fluids modified the sulfide mineralization to create broad haloes of metalliferous hydrous silicate minerals proximal to the Sudbury Breccia and in the footwall rocks. This study examines variations in the trace-element geochemistry of the breccia-matrix mineral assemblage developed adjacent to footwall mineralization in the North Range (Coleman Mine) and the South Range (Creighton Mine). The Sudbury Breccia is widely considered to have formed in a single event, contemporaneous with the meteorite impact, therefore it provides a relatively consistent baseline for studying subsequent metamorphic and hydrothermal processes, unlike the Archean Superior Province and Paleoproterozoic Southern Province, which experienced pre-impact alteration associated with tectonic and igneous activity. This study focused on examining the textural, chemical, and petrological changes recorded in biotites, amphiboles, chlorites, and Fe-oxides produced by late magmatic and post-magmatic sulfide mineralization and U-Pb age dates of titanite. Titanite-chlorite assemblages in the North Range footwall of the SIC overprint metalliferous assemblages adjacent to the McCreedy East 153 footwall ore body. They yielded an age of 1358 ± 78 Ma, which is interpreted to be associated with the waning effects of the 1450 ± 0.15 Ma Chieflakian orogeny. In the South Range at the Creighton Mine, the Sudbury Breccia hosting the Creighton Deep footwall ore body records a shift from ferro-hornblende to ferro-tschermakite amphibole. When coupled with variations in Ca/Ti in titanite and a U-Pb titanite age of 1616 ± 33 Ma, the assemblage is interpreted to reflect increasing temperature-pressure gradient towards shear zones that were active during the Mazatzalian orogeny, during which time the sulfide mineralization was remobilized. At both locations, biotite exhibits an increase in Tl content that relates to the Ni content of the host rocks and proximity to sulfide mineralization. This relationship may be produced by remobilization of metals during interaction between sulfide mineralization and hydrothermal fluids. Although not directly associated with sulfide emplacement, these signatures provide evidence for a larger geochemical halo around the mineral zone that may provide the basis for ranking the prospectivity of the footwall and possibly vectoring towards mineral zones.Keywords:
Breccia
Titanite
The accessory minerals are commonly used for P-T-t reconstruction of metamorphic complexes and were reported as controlling factor of trace elements distribution in various magmatic and metamorphic rocks. Apart from zircon and monazite, the data from titanite are also valuable geochronometer, geothermometer and tracer for magmatic and metamorphic processes are increasingly used in the last years (e.g. Aleinikoff et al., 2002; Frost et al., 2000). Titanites are often zoned and can record several magmatic and metamorphic events, due to its refractory behavior and long growth history. The titanite is widespread accessory phase in different lithologies from the Chepelare shear zone (Arda lithotectonic unit, Central Rhodope massif), which have a complex metamorphic history.
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Marbles containing high-pressure mineral assemblage was found from the Sanandaj-Sirjan metamorphic belt in the Nahavand area in western Iran. The high-pressure marbles occur as small bodies or lenses within pelitic schist layers and show compositional banding of carbonate- and silicate- rich bands. Textural analysis revealed two metamorphic stages. The early stage is testified by relicts of the minerals such as rounded jadeite-bearing diopside, epidote (clinozoisite), amphibole 1 (pargasite-edenite) and titanite 1. The second stage (main stage) documented to have phlogopite, chlorite, amphibole 2 (tremolite) and titanite 2. P-T-XCO2 estimates for the early stage of metamorphism give an average pressure, temperature and XCO2 of 13.5 kbar, 670 oC and 0.35, whereas the second stage has been constrained at P=3.8 kbar, T=500 oC and XCO2=0.45. The high-pressure mineral assemblage documented in the Nahavand area, were formed during the subduction stage, while the second metamorphic blastesis were recorded during the exhumation event.
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Titanite 是为因为它的相对高的 U， Th 和 Pb 的同位素的标明日期满足的 U-Pb 的一种理想的矿物质。这里，我们为用 193 nm ArF 激光脱离系统和 Agilent 7500a Q-ICP-MS titanite 标明日期的 U-Pb 开发了一种技术。titanite (BLR-1 和 OLT-1 ) 和锆石的标准(91500 并且 GJ-1 ) 被标明日期使用单个点和线光栅扫描分析方法。为了检查矩阵，效果， titanite (BLR-1 ) 和锆石(91500 ) 标准作为外部标准被分析。OLT-1 titanite 的加权的吝啬的 206Pb/238U 年龄是 1015
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Abstract Titanite can be found in rocks of wide compositional range, is reactive, growing or regrowing during metamorphic and hydrothermal events, and is generally amenable to U–Pb geochronology. Experimental evidence suggest that titanite has a closure temperature for Pb ranging from 550 to 650°C, and thus titanite dates are commonly interpreted as cooling ages. However, this view has been challenged in recent years by evidence from natural titanite which suggests the closure temperature may be significantly higher (up to 800°C). Here, we investigate titanite in an enclave of migmatitic gneiss included within a granite intrusion. The titanite crystals exhibit textural features characteristic of fluid‐mediated mass transfer processes on length scales of <100 µm. These textural features are associated with variation in both Pb concentrations and distinct U–Pb isotopic compositions. Zr‐in‐titanite thermometry indicates that modification of the titanite occurred at temperatures in excess of 840°C, in the presence of a high‐ T silicate melt. The Pb concentration gradients preserved in these titanite crystals are used to determine the diffusivity of Pb in titanite under high‐ T conditions. We estimate diffusivities ranging from 2 × 10 −22 to 5 × 10 −25 m 2 /s. These results are significantly lower than experimental data predict yet are consistent with other empirical data on natural titanites, suggesting that Pb diffusivity is similar to that of Sr. Thus our data challenge the wide‐held assumption that U–Pb titanite dates only reflect cooling ages.
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The Sullivan mine, in southeastern British Columbia, is one of the world's largest sediment-hosted, massive sulphide deposits. It has undergone at least one period of metamorphism since it was deposited in mid-Proterozoic times. Mineral textures within the deposit are predominantly of metamorphic origin. A well-constrained estimate of metamorphic conditions is required to understand how the original, depositional character of the orebody has been modified by metamorphism. Metamorphic conditions were estimated using multiequilibrium thermobarometric techniques involving silicate–carbonate–fluid equilibria. Peak metamorphic temperature constrained by calibration of the garnet–biotite Fe–Mg exchange equilibrium is 450 ± 50 °C. Lower temperature estimates from some samples are interpreted to record the temperature of cessation of garnet growth prior to the attainment of peak metamorphic temperature. Peak metamorphic pressure as determined from equilibria applicable to the assemblage garnet–biotite–muscovite–chlorite–calcite–quartz–fluid is 380 ± 100 MPa. The fluid composition accompanying this pressure estimate is [Formula: see text], [Formula: see text]. This estimate is particular to one sample and may not be representative for the deposit as a whole. Metamorphic fluids at the estimated P–T conditions would not have contained significant concentrations of C–O–H–S species other than H 2 O and CO 2 . Textural evidence and temperature–pressure results from a titanite-bearing metamorphosed mafic intrusion in the deposit suggest published titanite ages near 1330 Ma in the area of the mine represent the age of the peak metamorphic event. The results of this study carry tectonic implications for the Sullivan area, and may have application to other metamorphosed ore deposits and low-grade metamorphic settings.
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Titanite is a common accessory mineral in calc-alkailine granites,and may contain tin to various extents owing to similar crystal-chemical features between Ti 4+ and Sn 4+ .It thus may be considered as a useful mineral in studying tin granites(particularly oxidized tin granites) .This paper deals with a systematic study on titanite from three granites with known extensive tin mineralization(Qitianling,Huashan and Guposhan) and other three granites currently unknown for important tin mineralization(Lianyang,Dadongshan and Jiufeng) .Titanite from all these granites can form both at early-magmatic stage and during biotite chloritization at hydrothermal stage;late-magmatitc titanite is also found in Qitianling,Huashan and Jiufeng.Electron-microprobe results reveal distinct compositions among three types of titanite.Early-magmatic titanite contains trace of tin(generally1% SnO2) ,whereas late-magmatic titanite with 3 to 26%SnO2 can be found in Qitianling,Huashan and Jiufeng.Hydrothermal titanite is typified by high Al and F contents.Comparison of SnO2 contents for titanite from six granites shows that titanite,either magmatic or hydrothermal,from three tin granites(Qitianling,Huashan and Guposhan) is rich in SnO2 with averages0.4%,revealing their strong tin mineralizing potential;titanite of Lianyang and Dadongshan granites is very poor in SnO2(0.1%) ,consistent with their barren feature.However,similar to Huashan titanite,the magmatic titanite from Jiufeng granite contains up to 3%SnO2,and hydrothermal one up to 2%SnO2.Such tin enrichment in titanite might imply higher tin potential of the Jiufeng granite,possibly favorable for further tin exploration.The present results demonstrate that titanite may act as a simple,but useful mineral criterion of tin mineralizing potential in granites.
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The Sullivan mine, in southeastern British Columbia, is one of the world's largest sediment-hosted, massive sulphide deposits. It has undergone at least one period of metamorphism since it was deposited in mid-Proterozoic times. Mineral textures within the deposit are predominantly of metamorphic origin. A well-constrained estimate of metamorphic conditions is required to understand how the original, depositional character of the orebody has been modified by metamorphism. Metamorphic conditions were estimated using multiequilibrium thermobarometric techniques involving silicate- carbonate - fluid equilibria. Peak metamorphic temperature constrained by calibration of the garnet-biotite Fe-Mg exchange equilibrium is 450 + 50°C. Lower temperature estimates from some samples are interpreted to record the temperature of cessation of garnet growth prior to the attainment of peak metamorphic temperature. Peak metamorphic pressure as determined from equilibria applicable to the assemblage garnet -biotite -muscovite -chlorite - calcite - quartz -fluid is 380 f 100 MPa. The fluid composition accompanying this pressure estimate is XHzo = 0.38, X,,, = 0.62 + 0.07. This estimate is particular to one sample and may not be representative for the deposit as a whole. Metamorphic fluids at the estimated P- T conditions would not have contained significant concentrations of C -0-H -S species other than H,O and CO,. Textural evidence and temperature-pressure results from a titanite-bearing metamorphosed mafic intrusion in the deposit suggest published titanite ages near 1330 Ma in the area of the mine represent the age of the peak metamorphic event. The results of this study carry tectonic implications for the Sullivan area, and may have application to other metamorphosed ore deposits and low-grade metamorphic settings.
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