Metamorphic history of the Hemlo gold deposit from Al2SiO5 mineral assemblages, with implications for the timing of mineralization

1999 ◽  
Vol 36 (1) ◽  
pp. 33-46 ◽  
Author(s):  
Wayne G Powell ◽  
David RM Pattison ◽  
Paul Johnston
Keyword(s):  
Gold Deposit ◽  
Quartz Veins ◽  
Metamorphic History ◽  
Fluid Infiltration ◽  
Mineral Assemblages ◽  
Metamorphic Assemblage ◽  
The Matrix ◽  
History Of ◽  
T Path ◽  
Late Growth

Textural relations between Al2SiO5 phases, and deformation fabrics, provide constraints on the metamorphic history of the Hemlo gold deposit. Kyanite in the deposit is most common within and on the margins of boudinaged quartz ± realgar veins, and less commonly as rotated porphyroblasts within the matrix of schistose rocks. Kyanite predates the main (D2) schistosity. Sillimanite postdates kyanite, occurring irregularly as discrete knots and foliae that run parallel to, but sometimes cut across, the principal (D2) foliation, indicating that sillimanite postdates the D2 foliation. We regard kyanite to be part of the peak metamorphic assemblage, with sillimanite representing a partial later overprint most likely related to fluid infiltration. Rare andalusite occurs in two associations: as late-stage, clean, idioblastic crystals; and as large, fractured grains, locally overprinted by sillimanite, in boudinaged quartz-realgar veins. We suggest two possible origins for this second form of andalusite, one involving generally late growth, the second involving early growth prior to the development of peak metamorphic kyanite. Although not unambiguous, we prefer the second scenario. P-T conditions from petrogenetic grid constraints, and new geothermobarometric estimates, indicate 6-7 GPa, 600-650°C for the peak kyanite grade metamorphism (ca. 2677 Ma?), and 4-5 GPa, 600°C for the later sillimanite overprint (ca. 2672 Ma?). We see these two events as part of an evolving P-T path in a single metamorphic event. In our early andalusite scenario, the andalusite may have formed from pyrophyllite breakdown at 2-4 GPa, 450°C, possibly associated with emplacement of the regional suite of granodiorite plutons (ca. 2686 Ma). Late andalusite formed sporadically on the retrograde path. The occurrence of deformed andalusite and aligned kyanite in and on the margins of boudinaged auriferous realgar-stibnite-quartz veins provides evidence in support of a premetamorphic mineralization event.

A retrogressive sapphirine-cordierite-talc paragenesis in a spinel-orthopyroxenite from southern Karnataka, India

1993 ◽  
Vol 57 (387) ◽  
pp. 273-288 ◽  
Author(s):  
C. R. L. Friend ◽  
A. S. Janardhan ◽  
N. Shadakshara Swamy
Keyword(s):  
Dharwar Craton ◽  
Amphibolite Facies ◽  
Coarse Grained ◽  
Cooling History ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
Igneous Origin ◽  
Mineral Assemblages ◽  
History Of ◽  
Granoblastic Texture

AbstractWithin amphibolite facies Peninsular gneisses in the south of the Dharwar craton, units of Sargur supracrustal rocks contain ultrabasic enclaves. One of these enclaves is an orthopyroxenite which comprises bronzite, spinel and minor phlogopite preserving coarse-grained, relic textures of probable igneous origin. After incorporation into the gneisses the enclave evolved through several distinct stages, elucidation of which allow an assessment of its metamorphic history.Firstly, deformation during closed system, anhydrous recrystallisation caused the coarse-grained textures to be partially overprinted by similar mineral assemblages but with a granoblastic texture. Secondly, open system hydration caused retrogression of the bronzite to alumino-gedrite at the margins of the enclave. Subsequently, the penetration of these fluids along grain boundaries caused reactions between spinel and bronzite to produce reaction pockets carrying assemblages of peraluminous sapphirine associated with cordierite and talc. The differences in the mineral assemblages in each pocket coupled with slight variations in their chemistry, suggest that equilibrium did not develop over the outcrop. Because sapphirine + magnesite is present in some pockets, it is evident that CO2 was also a component of the fluid.Phase relations from the MASH portion of the FMASH system, to which the chemistry of the reaction pockets approximates, suggest that the hydrous metamorphism causing the changes depended upon the assemblage enstatite + spinel + vapour which exists at PT conditions above the position of I16, ∼760°C at 3 kbar and below I21 at ∼765°C at 5.6 kbar (Seifert, 1974, 1975), where sapphirine is replaced by kornerupine. The suggested path of reaction occurred between I18 and I21. Subsequent reactions related to I20 cause the formation of cordierite. Talc formation has to be modelled in a different reaction grid.The metamorphism recorded by these reactions is thus at a maximum of amphibolite facies and is interpreted to have formed during the uplift and cooling history of the gneiss complex when hydrous fluids were free to migrate. Given the complex high-grade metamorphic history of this part of the Dharwar craton this event is likely to be late Archaean or Palaeoproterozoic in age.

scholarly journals Controls of metamorphic grade in shear belts

1979 ◽  
Vol 89 ◽  
pp. 47-62
Author(s):  
J Grocott
Keyword(s):  
Vertical Displacement ◽  
Metamorphic Grade ◽  
Perfect Equilibrium ◽  
Horizontal Gradients ◽  
Metamorphic History ◽  
Mineral Assemblages ◽  
History Of ◽  
Set Up ◽  
The Relationship ◽  
Shear Belt

The relationship between metamorphic grade and deformation is examined for shear belts occurring in Precambrian shields. A particular case, where isotherms have fallen continuously relative to an originally horizontal datum surface, for some time prior to the initiation of the shear belt and throughout its life, is examined in detail. Such behaviour of isotherms appears to be common. A type of syn-tectonic metamorphic boundary occurring within shear belts and not coinciding with a strain gradient is discussed in detail. Such boundaries are called active facies boundaries, as mineral assemblages on each side tend to maintain perfect equilibrium with metamorphic conditions during deformation. The orientation of active facies boundaries depends on the vertical displacement rate. In ductile thrust zones horizontal gradients in metamorphic conditions can be set up, and folIowing erosion once active facies boundaries may be exposed. The metamorphic history of rocks in such zones will vary vertically, and, under certain circumstances, laterally. A model is set up to predict these variations, and is applied to the northem boundary of the Ikertoq shear belt, western Greenland.

XII.—Petrology and Petrogenesis of some Garnetiferous Peridotites

1963 ◽  
Vol 65 (12) ◽  
pp. 251-314 ◽  
Author(s):  
M. J. O'Hara ◽  
F. H. Stewart
Keyword(s):  
South Africa ◽  
Crystalline Rocks ◽  
Chemical Analyses ◽  
X Ray ◽  
Metamorphic History ◽  
Igneous Origin ◽  
Mineral Assemblages ◽  
History Of ◽  
Reliable Interpretation ◽  
Recent Experimental Work

SynopsisGarnetiferous peridotite masses which occur among gneisses in the Tafjord district of Norway are cold intrusions emplaced as crystalline rocks late in the metamorphic history of the region. No relationship other than similarity of mineral facies can be established between the peridotites and the eclogite bodies in the surrounding gneiss. Chemical analyses of twelve olivines, fourteen orthopyroxenes, nine chrome diopsides, nine garnets, three amphiboles and two rocks are presented, representing material from the Tafjord and Almklovdalen districts of Norway, a garnetiferous peridotite mass near Bellinzona, Switzerland, and the garnet-peridotite inclusions in the kimberlite pipes of South Africa. Optical and X-ray data for the analyzed and some unanalyzed assemblages are also presented. The mineral assemblages of these rocks are compared with each other, and with data from the peridotites of layered tholeiitic intrusions, alpine-type peridotites and the peridotite nodules in basalts. The garnet-peridotites of Norway, Switzerland and South Africa are believed to be little altered fragments of the mantle, whereas the peridotite nodules in basalts and the alpine-type peridotites are believed to be of igneous origin. Examination of the distribution of cations between the coexisting phases suggests that there are too many variables to permit a reliable interpretation of the results.The orthopyroxenes from the garnetiferous peridotites are not rich in A1203, contrary to expectations based upon recent experimental work.

scholarly journals Mineralogy of the Vorontsovskoe gold deposit (Northern Urals). Part 1: history of study, mineral assemblages, list of minerals

2020 ◽  
pp. 3-34
Author(s):  
A.V. Kasatkin ◽  
S.Yu. Stepanov ◽  
M.V. Tsyganko ◽  
R. Skoda ◽  
Nestola F. ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Analytical Methods ◽  
Northern Urals ◽  
Mineral Assemblages ◽  
S Mineralization ◽  
History Of ◽  
Ore Types ◽  
Geological Position ◽  
History Of Study ◽  
Exhaustive List

This work is the frst paper in a series of publications dedicated to mineralogy of the Vorontsovskoe gold deposit in the Northern Urals. The deposit is unique for both Russia and world with regard to the diversity and originality of Tl–Hg–Mn–As–Sb–S mineralization. Based on available literature and our data, we compiled an exhaustive list of 209 mineral species of the deposit, including eight new minerals found by the authors: vorontsovite, ferrovorontsovite, tsygankoite, gladkovskyite, luborzakite, pokhodyashinite, gungerite and auerbakhite. In addition, 40 and 89 minerals are found for the frst time in Russia and the deposit, respectively. Systematic studies of ores revealed nine main mineral assemblages, seven of which are confned to carbonate breccias. They contain more than 70 rare sulfdes, tellurides and sulfosalts including 30, 12 and 9 minerals, where Tl, Hg and Mn are species-defning elements, respectively. In this paper, we characterize the history of study of the deposit, its geological position and structure, ore types, mineral assemblages, and analytical methods.

Petrography and phase equilibrium modeling of Paleoproterozoic metapelite in the Kuluktag area of Tarim Craton

2021 ◽  
Author(s):  
Yu Guo
Keyword(s):  
Phase Equilibrium ◽  
Chemical System ◽  
Equilibrium Modeling ◽  
Fine Grained ◽  
Metamorphic Basement ◽  
Mineral Assemblages ◽  
The Matrix ◽  
Tarim Craton ◽  
T Path ◽  
Tectonothermal Event

<p>  The Kuruqtag area, located at the northeastern margin of the Tarim Craton, where the Precambrian metamorphic basement exposed, is ideal for studying the Precambrian geological evolution of the Tarim Craton. Previous zircon U-Pb chronology studies revealed that the metamorphic basement recorded a Paleoproterozoic tectonothermal event and suggested it associates with the Paleoproterozoic Nuna/Columbian supercontinent convergence event. However, the extensive range of metamorphic ages obtained from different studies (ranging from 1750-2000 Ma) and the lack of detailed P-T path corresponding to different metamorphic ages make it difficult to constrain the evolutionary framework of the Tarim craton during the Paleoproterozoic, which in turn affects future comparative regional studies.</p><p>  To constrain the P-T path, in this study, we performed detailed petrography, mineral chemical, and phase equilibrium modeling of metapelite collected from the khondalite series in the western part of the Kuruqtag (a garnet-sillimanite-cordierite-biotite gneiss with metamorphic age ~1850 Ma) and obtained the following results.</p><p>  Through petrographic studies, at least three phases of mineral assemblages can be used to invert the P-T path experienced by the metapelite. They are    M1 (peak metamorphic stage):represented by fine-grained biotite remnant (Bi Ⅰ) + fine-grained plagioclase(Pl Ⅰ) and quartz+ Ilmenite + , occurring as inclusions within the metamorphic garnet, and equilibrated mineral assemblages is: Grt(core) + Bi Ⅰ + Sill + Kfs + Pl Ⅰ + Qz + Ilm. M2 (isothermal depression stage), represented by cordierite occurring in the garnet rim or with spinel in the matrix, inferred equilibrated mineral assemblages is Grt(rim)+Bi Ⅰ +Cd+Kfs+Pl ⅠⅠ+Ilm+Sp.M3 (isothermal depression stage), is marked by the appearance of new growth of biotite(Bi ⅠⅠ) and the conversion of Sill to And.<span> </span></p><p>The P-T conditions for the mineral assemblage evolution (M1 → M3) are constrained by a P-T pseudosection constructed in the Na2O -CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O- TiO2-O2 chemical system. The resulting P-T path is clockwise from the M1 stage (840°C, 4 Kbar) through the isothermal depression path to M2 (840-850°C,5 Kbar) and then through the near-isobaric cooling path to the M3 stage (650°C, 3.5-4 Kbar).</p>

scholarly journals Mineral chemistry of eclogites to investigate the evolutionary metamorphic history of UHP rocks from Tso-Morari region, Ladakh, India

2010 ◽  
Vol 40 ◽  
pp. 13-20
Author(s):  
Rameshwar Rao ◽  
Hakim Rai
Keyword(s):  
High Pressures ◽  
Mineral Chemistry ◽  
Textural Features ◽  
Mineral Inclusions ◽  
Metamorphic History ◽  
Facies Metamorphism ◽  
History Of ◽  
T Path ◽  
Si Content ◽  
Tso Morari

Micro textures of metabasics from the Tso-Morari region, Ladakh were studied in order to understand the evolutionary metamorphic history of eclogites. The mineral chemistry, paragenesis of mineral inclusions in garnet, and zoning in omphacite, garnet and amphibole suggest three main metamorphic stages: (i) an eclogite stage with late blueschist facies metamorphism, (ii) a medium-pressure amphibolite facies stage, and (iii) a low-pressure amphibolite to greenschist facies stage. The high Si content in phengite, presence of rutile besides almandine-rich garnet and omphacite in eclogites indicate the attainment of high pressures. Also, the textural features and composition of amphiboles indicate that blueschist facies conditions represented by growth of glaucophane at high pressure and low temperature were followed by a lower-pressure stage of metamorphism represented by partial and in some cases complete reaction of glaucophane to calcic green amphibole such as magnesio-hornblende. The relationships define a clock-wise P-T path with the involvement of an isothermal uplift path for the eclogites and associated garnet-amphibolites of Tso-Morari region.

scholarly journals Thermoluminescence as a technique for determining the nature and history of small solar system particles

2011 ◽  
Vol 38 (3) ◽  
pp. 272-281
Author(s):  
Jonathan Craig ◽  
Derek Sears
Keyword(s):  
Solar System ◽  
Radiation Dosimetry ◽  
Ordinary Chondrite ◽  
Small Particles ◽  
Fundamental Properties ◽  
Metamorphic History ◽  
The Matrix ◽  
History Of ◽  
Terrestrial Age

Abstract The thermoluminescence phenomenon has been used for pottery dating and radiation dosimetry for sixty years and for forty years has been applied to the study of meteorites, being successful in quantifying metamorphic histories and providing new insights into terrestrial age and orbits. Here we review some of the fundamental properties of thermoluminescence with particular focus on the study of small extraterrestrial particles. We suggest that natural TL data can be used to identify the burial and release history of cometary particles and that induced TL measurements can provide in-sights into the mineralogy of particles (even when largely amorphous) and the metamorphic history of those particles. We illustrate the use of TL to study small particles by describing recent studies on micrometeorites and 10–100 μm fragments taken from the matrix of a meteorite Semarkona which is type 3.0 ordinary chondrite.

Chemical zonation and relative timing of growth sections in garnets from eclogites of the Leaota Massif, South Carpathians

2006 ◽  
Vol 70 (6) ◽  
pp. 655-667 ◽  
Author(s):  
G. Săbău ◽  
E. Negulescu ◽  
H.-J. Massonne
Keyword(s):  
Morphological Characteristics ◽  
Garnet Growth ◽  
Growth Stages ◽  
Chemical Zoning ◽  
Metamorphic History ◽  
Growth History ◽  
Mineral Assemblages ◽  
History Of ◽  
Partial Resorption ◽  
Zonation Patterns

AbstractWe have investigated the chemical zoning of garnet in three texturally different eclogite types from the Leaota Massif, Romania, to test the various zonation patterns of Ca, Fe, Mg and Mn as indices of time-lines in porphyroblastic garnets. Mn zonation was found to mark various growth stages very well. It indicates in each of our three case studies a complex growth history dominated by multiple nucleation and coalescence, but also interrupted by partial resorption, as shown by morphological characteristics. Chemical variations of the main elements in garnet during prograde high-pressure metamorphism define time-lines other than those of Mn which decrease, highlighting the stages of porphyroblastic growth. In particular, the Ca/Mn, Mg/Mn and Mg/Fe ratios are useful in late growth stages, when low Mn contents and radial gradients do not allow a satisfactory resolution of Mn time-lines. These ratio-based time-lines further substantiate the potential of Mn time-lines in revealing non-concentric porphyroblastic growth. This is important in order to correctly relate garnet growth stages to stable mineral assemblages, a prerequisite for a reliable derivation of the metamorphic history of the host rock.

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