Papers by Anthony Fallick
Millpress eBooks, Aug 1, 2003
Two epithermal environments have been identified in the Miocene Palai-Islica Au-Cu deposit: A) In... more Two epithermal environments have been identified in the Miocene Palai-Islica Au-Cu deposit: A) Intermediate sulphidation, hosted mainly in quartz veins, comprises pyrite, chalcopyrite, sphalerite and galena as the major sulphides, which are accompanied by a variety of Ag-bearing accessory minerals. Au-Ag alloys are the only gold-bearing phase. The veins are enclosed by sericitic and chloritic alteration. Fluid inclusions in quartz, sphalerite and calcite give T h between 118-453 ºC, and salinities between 0.2-51.4 wt.% NaCl eq, with high salinities being related to high-grade mineralisation. Stable isotopes indicate magmatic and marine fluids. B) High sulphidation consists of massive host rock silicification with disseminated pyrite and minor chalcocite, covellite, native copper and native gold. The surrounding alteration is advanced argillic/argillic in style. Fluids have T h between 224-381 ºC have salinities between 0.4 and 41.1 wt.% NaCl eq. The stable isotope data demonstrate the dominance of magmatic fluids, and disproportion processes.
Isotope chemostratigraphy and detailed mapping of high-grade marble sequences 209 Analytical tech... more Isotope chemostratigraphy and detailed mapping of high-grade marble sequences 209 Analytical techniques are described in Appendix 1. The study area is located north of Ofotfjorden and Herjangsfjorden and south of Astafjorden (Figs.
Arabian Journal of Geosciences, 2022
The Khenchela massif, northeast Algeria, belongs to the eastern Saharan Atlas that extends northe... more The Khenchela massif, northeast Algeria, belongs to the eastern Saharan Atlas that extends northeasterly from the Aurès Chain, through the Mellegue mountains, to the Tunisian Atlas. This massif is characterized by sandstone and marl outcrops of the Lower Cretaceous that are overlain by limestone and marl of the Upper Cretaceous. The anticline structure was subjected to several NW–SE to WNW-ESE-directed major normal faults that split the massif into a number of mega-blocs. Triassic evaporitic lithologies crop out as diapirs at the northeastern and southwestern parts of the anticline. The Ain Mimoun region, located on the northern flank of the Khenchela anticline, is composed of Albian-Aptian sediments that host the barite veins of the so-called ‘Mizab barite deposit’. This deposit, which is currently exploited, consists of a dozen main veins composed mainly of barite with quartz, calcite, ankerite and rare base-metal sulphide mineralisation (galena, sphalerite, tennantite and chalcopyrite). The host sedimentary rocks were subjected to severe silicification and dolomitisation processes. Barite shows a number of aspects: banded, massive and stockwork; in all cases, barite shows tabular crystals of several millimeters in size. Microthermometric measurements carried out on primary two-phase fluid inclusions in barite crystals (barite I and barite II) and gangue quartz gave homogenization temperatures between 155 and 225 °C and salinities of 17.6 to 25.9% NaCl eq. The data show at least three types of mixing fluids that deposited the sulphate-sulphide mineralisation. δ34S values of barite are between + 17.9 and + 27.6‰ and the δ34S values of the associated sulphides vary between − 9.2 and + 3.0‰. These data indicate that the most likely source of sulphur is the sulphates (gypsum) of the Triassic evaporitic formation (δ34S ranging between + 11.5 and + 13.4‰). Thermochemical sulphate reduction is the most probable process by which H2S was produced, although relatively large negative δ34S values point to a possible minor contribution from the biogenic sulphate reduction process. Carbon and oxygen isotopic compositions of gangue carbonates (calcite and ankerite) and oxygen of gangue quartz indicate a common source of the mineralising fluid. Calculated δ18Ofluid from quartz oxygen isotope data varies between + 6 and + 12‰, indicating deep-seated brines with minor contribution from a surface water component. The relatively hot and saline fluids have most likely migrated upward in several pulses during the Triassic halokinesis and compressive/distensive Atlassic (Eocene) and Alpine (Miocene) tectonic phases. The Mizab barite deposit exhibits geological, fluid inclusion and isotopic features similar to those of the peridiapiric mineralisation of northeastern Algeria and Tunisia.
The Canadian Mineralogist, 2017
Gem-quality (cabochon) ruby-bearing occurrences (here termed PAR-1 and PAR-5) located near Parane... more Gem-quality (cabochon) ruby-bearing occurrences (here termed PAR-1 and PAR-5) located near Paranesti, north eastern Greece have been systematically studied for the first time in this paper. Tectonically, the occurrences are located within the Nestos Shear Zone (NSZ). The NSZ separates two distinct geological units. The Rhodope Terrane is a heterogeneous unit of gneisses, mafic, ultramafic, and meta-sedimentary rocks in the hanging wall. The footwall Pangaion-Pirin Complex consists of marbles and acid gneisses of a Mesozoic carbonate platform on pre-Mesozoic continental basement. In this paper, a range of petrographic and geochemical techniques were used to determine (1) any similarities and differences to other mafic-ultramafic hosted ruby deposits worldwide; (2) distinctive geochemical fingerprints for Paranesti; and (3) the likely P-T conditions of formation. Detailed petrographic and whole-rock analyses utilizing ICP-MS, XRF, and XRD have found the Paranesti corundum to be of a mafic/ultramafic protolith with approximately 40 wt.% SiO 2 , 16 wt.% Mg, 11000 ppm Cr, and 440 ppm Ni. EMPA major element analysis determined the mineral inclusions within the corundum grains to be picotite and hercynite spinels. Pargasite is the dominant amphibole within the corundum-bearing amphibole schist host. The surrounding non-corundum bearing chlorite schist mainly comprises clinochlore. Petrographic examination of the mineral assemblages within the corundum-bearing schists revealed strong fracturing and alignment (parallel to the main regional foliation) of the corundum grains and margarite reaction rims around the corundum. The surrounding non-corundum amphibolites also contain anorthite, along with relict sillimanite, kyanite, and chlorite/muscovite/epidote overprinting. Detailed LA-ICP-MS trace element analysis of the color range of corundum from the two occurrences showed the corundum to be mainly of metamorphic origin, though pale rubies from PAR-5 suggest some metasomatic influence. The corundum displays distinctive geochemical locality signatures, with a combination of high Cr (average 2300 ppm with 15% sample points on core positions .5000 ppm and maximum 8600 ppm); high Si (average 1400 ppm with 40% over 1500 ppm and maximum 2500 ppm), low Mg (average 30 ppm), and very low V, Ti, and Ga. Based on the literature for similar occurrences, and the mineral assemblages observed at Paranesti, the estimated P-T conditions of corundum formation are ,7 kbar and ,750 8C, similar to the mafic African amphibolite-hosted rubies. This study has found the Paranesti occurrences to be most similar to the Winza, Tanzania ruby deposit, whilst there are some similarities to other high-Cr ruby deposits, primarily the Fiskenaesset, Greenland and metamorphic amphibolitic schist hosted African deposits. The Paranesti corundum most likely formed during regional amphibolite facies metamorphism which created the Nestos Shear Zone, along with a lesser influence (primarily observed in the PAR-5 occurrence) of more localized metasomatism. Subsequent multiple greenschist facies retrogression of the occurrences resulted in the current-day host amphibole-chlorite schist assemblages.
Resumen de la ponencia presentada en el VI Congreso Geológico de España (Zaragoza).En el presente... more Resumen de la ponencia presentada en el VI Congreso Geológico de España (Zaragoza).En el presente trabajo se describen las características texturales, químicas e isotópicas de la jarosita y de distintos sulfatos relacionados del depósito epitermal de Au-Cu de Palai-Islica (Almería) y se discute su significado e implicaciones genéticas.Barite and great quantities of Fe±Al sulfates (jarosite, natrojarosite, natroalunite and aluminite) together gypsum characterize the latest stages of the Au-Cu, Tertiary volcanic related, epithermal mineralisation of Palai-Islica. The Fe±Al sulfates present at the top of the mineralisation have a complex chemistry: an almost complete Na+-K+, an incomplete Fe3+-Al3+ solid solutions and uncommon substitution vector (PAsPbS-2(NaK)-1). The textural relations show an AlFe, accompanied for a pH decrease, and a more hypothetical KNa trends. The S and O isotope study is in accordance with a evolution from warm marine waters (± magmatic input) which precipitate barite after the ore episode to meteoric relatively cool waters. The product of these last waters are gypsum and the Fe±Al sulfates. As show the isotope results, the source of S for this sulfates is the oxidation of sulfides. In addition, a H2S input from hydrothermal fluids has also been deduced to exist since the great abundance of the sulphates, the scarcity of sulfide oxidation features and the presence of fluid inclusions in gypsum that not homogenize until gypsum dehydration.Departamento de Mineralogía y Petrología (Universidad de Granada)Trabajo financiado por BTE 2001-3308 y 2003-06265 (DGCYT) y RNM131 (Junta de Andalucía)
Norsk Geologisk Tidsskrift, 2000
The ca. 2000 Ma Tulomozerskaya Formation, Russian Karelia, is composed of an 800 m-thick magnesit... more The ca. 2000 Ma Tulomozerskaya Formation, Russian Karelia, is composed of an 800 m-thick magnesite-stromatolite-dolostone-'red bed' succession with the most 13 C-rich dolostones (up to 18% V-PDB) that have ever been reported. Terrigenous 'red beds' are developed throughout the sequence and represent three main depositional settings: (1) a braided fluvial system over a lower energy, river-dominated coastal plain, (2) a low-energy, barred lagoon or bight, and (3) a non-marine, playa lake. A significant component of the sequence consists of biostromal and biohermal columnar stromatolites accreted in shallow-water, low-energy, intertidal zones, barred evaporitic lagoons and peritidal evaporitic environments. Only a small portion of stromatolites might have been accreted in relatively 'open' marine environments. The red, flat-laminated, dolomitic and magnesite stromatolites formed in evaporative ephemeral ponds, coastal sabkhas and playa lakes. Tepees, mudcracks, pseudomorphs after calcium sulphate, halite casts, and abundant 'red beds' in the sequence suggest that (1) terrestrial environments dominated over aqueous, and (2) partial or total decoupling took place between the stromatolite-dominated depositional systems and the bordering sea. The greatest enrichment in 13 C occurs in the playa magnesite (up to 17.2%) and in the laminated dolomitic stromatolites accreted in ephemeral ponds (up to 16.8%), whereas the dolostones from more open environments are less rich in 13 C (5.6 to 10.7%). The isotopic shift (ca. 5%) induced by global factors (i.e. accelerated accumulation of organic material in an external basin) was augmented by that driven by a series of local factors (restriction, evaporation, biological photosynthesis). The latter enhanced a global 13 C value due to an isotopic disequilibrium between atmospheric CO 2 and dissolved inorganic carbon in the local aquatic reservoirs precipitating the carbonate minerals. The interplay between global and local factors should be taken into account when interpreting the Palaeoproterozoic carbon isotope excursion and its implications.
ABSTRACT Gem deposits are rare because in general the conditions that promote their formation are... more ABSTRACT Gem deposits are rare because in general the conditions that promote their formation are unusual and thus worthy of scientific study. Recently, modern geological and analytical techniques have been applied to gem occurrences worldwide, and our models and understanding of their formation are being radically altered. This short course volume looks at gemstones from a geological perspective and reviews our current understanding of diamond, ruby, sapphire, and emerald deposits, but will also examine the lesser known coloured gems.
Earth and Environmental Science Transactions of the Royal Society of Edinburgh
With their extensive fossil record and shells of stable low-Mg calcite, rhynchonelliform brachiop... more With their extensive fossil record and shells of stable low-Mg calcite, rhynchonelliform brachiopods are attractive Sources of climate information via seawater temperature proxies such as stable oxygen isotope composition. In Terebratalia transversa (Sowerby) there is a progression towards oxygen isotope equilibrium in the calcite of the innermost secondary layer. This study confirms the lack of any vital effects influencing oxygen isotope composition of T transversa, even in specialised areas of the innermost secondary layer. Calcite Mg/Ca ratio is another potential seawater temperature proxy, that has the advantage of not being influenced by salinity. Mg concentrations measured by electron microprobe analyses indicate that there is no concomitant decrease in Mg concentration towards the inner secondary layer, associated with the progressive shift towards oxygzen isotope equilibrium. Mg distribution is heterogeneous throughout the shell and correlates with that of sulphur, which ma...
ABSTRACT No abstract available.
ABSTRACT A number of sedimentary formations deposited globally around 2.0 Ga ago are characterise... more ABSTRACT A number of sedimentary formations deposited globally around 2.0 Ga ago are characterised by high abundances of organic carbon. These formations often contain occurrences of highly concentrated, matured organic material representing metamorphosed oil, now pyrobitumen. Apart from their common names pyrobitumen or anthraxolite, different terminology has been used for these rocks within the pertinent literature, including shungite, thucolite, or Precambrian “coal”. Given their long and frequently complex geologic history, these sedimentary formations exhibit a variable and sometimes substantial degree of metamorphic (thermal) overprint. Consequently, many of them show undisputable signs of thermal mobilisation, migration and likely loss of hydrocarbons/bitumen. This includes the so-called shungite rocks on the Fennoscandian Shield.
Many, if not all, of the long-term fluctuations in geological processes operating on Earth’s surf... more Many, if not all, of the long-term fluctuations in geological processes operating on Earth’s surface are tectonically driven and related to the interplay of plate tectonics and deep mantle dynamics resulting in supercontinental cycles and (super)plume events (Condie et al. 2001; Condie 2004). These processes include the amalgamation, dispersal, collision and geographic position of major land-masses which dictate volcanic and hydrothermal activities, changes in sea level and the global patterns of ocean circulation, thermal isolation of continents, climate change, rate of continental weathering and its influence on seawater composition, and atmospheric oxygen budget via control of burial and recycling of carbon and sulphur. Further, all of these are reflected in biological processes. However, well-documented and well-constrained examples of this conceptual model have been developed and tested largely on Phanerozoic rocks (Valentine and Moores 1970; Fischer 1984; Marshall et al. 1988; Hardebeck and Anderson 1996; Berner 2006; Rampino 2010). Although there have been a number of attempts to apply such concepts to “Deep Time”, in particular, the Palaeoproterozoic (Nance et al. 1986; Windley 1993; Lindsay and Brasier 2002; Condie et al. 2009), testing and verification of the models is challenging. The existence of continental masses, their palaeogeography and sizes in the late Archaean-early Palaeoproterozoic remain hypothetical and robust plate reconstructions are hampered by the small number of reliable palaeomagnetic data (Evans and Pisarevsky 2008).
Ore Geology Reviews, 2013
Radically nonuniformitarian modes of Earth System behaviour have been hypothesized as hallmarks o... more Radically nonuniformitarian modes of Earth System behaviour have been hypothesized as hallmarks of Neoproterozoic Earth history. In particular, severe climatic extremes (worldwide glaciations marked by globally frozen oceans to ultra-greenhouses) are envisaged to have occurred at least twice; these inferred harsh climates are invoked as a potential driving mechanism for biospheric evolution. Such hypotheses are intellectually elegant and their vividness grabs public attention, but how strictly do they adhere to the observational facts of the rock record? Here we show examples of Neoproterozoic glacigenic successions that imply severe, but not catastrophic climate change. The first example is the Port Askaig Tillite of Scotland. This unit was deposited in low latitudes (<30^o) and records the older ("Sturtian") glacial episode. Importantly, it contains evidence for freeze-thaw cycles on a number of time scales and, when combined with similar features observed in glacial ...
Transactions of the Royal Society of Edinburgh: Earth Sciences, 1993
ABSTRACTStable isotope data from the East Kirkton succession are used to elucidate the extent of ... more ABSTRACTStable isotope data from the East Kirkton succession are used to elucidate the extent of hot-spring influence in the palaeoenvironment by constraining conditions of deposition of the silica and the formation of sulphides.Petrographically silica occurs as chert laminae thought to be primary, and as patchy chert considered as replacive. No evidence for biogenic silica was observed. For 20 silica samples δ18O was measured for structural oxygen and δD for bound water. δ18O(SMOW)varied between +21 and +27‰ with no sample groupings related to petrography. The range in δD(SMOW)was from −50 to −90‰ with lower values characterising replacive or altered silica; water contents of both petrographic groups were similar. A plot of δ18O versus δD for the laminated primary silica defines a grouping about the line defined by Scottish agates (Fallicket al.1985). This suggests for the unaltered silica a formation temperature of about 60°C and a fluid containing a strong component of meteoric w...
Transactions of the Royal Society of Edinburgh: Earth Sciences, 1994
Mineralisation associated with Late Caledonian metaluminous granitoids in the Grampian Terrane ha... more Mineralisation associated with Late Caledonian metaluminous granitoids in the Grampian Terrane has been investigated using stable isotope, fluid inclusion and mineralogical techniques.A porphyry-stock-related style of mineralisation in the Grampian Terrane is characterised by a stockwork of veinlets and disseminations in dacite prophyries, consisting of quartz, dolomite, sulphides and late calcite, and well-developed wallrock alteration dominated by zones of phyllic, sericitic and propylitic alteration. On the basis of δ34S (+0·4±l·0‰), δ13C (−5·7‰ to + l·4‰) and δ18O (+10·8‰ to +19·9‰) it is likely that initial mineralising components were orthomagmatic with an input of external fluids during the later parageneses. Fluids were saline, boiling (up to 560°C), deficient in CO2, and ore deposition took place at depths of less than 3 km.Plutonic-hosted mineralisation in appinites, diorites, tonalites and monzogranites is commonly represented by sporadic disseminations and occasional vei...
Mineralogy and Petrology, 1996
Polymetallic major veins of the West Carbery district (County Cork) are compared with the nearby ... more Polymetallic major veins of the West Carbery district (County Cork) are compared with the nearby stratiform-disseminated copper mineralization in metasedimentary rocks, containing minor veins (metamorphic quartz veins and veinlets). These stratiform deposits are hosted by non-marine Devonian sediments (Old Red Sandstone), metamorphosed in the Hercynian orogeny. In sulphides from the stratiform deposits and minor veins, isotopic compositions of sulphur (334S) range from -21.00 to + 5.14%o , consistent with the vein sulphide being remobilized stratiform-disseminated sulphide, and the latter being of diagenetic bacteriogenic origin. Sulphate (barite), found in veins separate from the sulphides, has 63~S + 12.3 to + 15.7%o consistent with groundwater origin. In minor-vein quartz, fluid inclusions have homogenization temperatures consistent with trapping under the estimated peak-metamorphic conditions (300-400 °C, 1-3 kbar). In the major veins, sulphide 634S (-15.8 to -4.2%o ) suggest remobilization of diagenetic sulphide. Oxygen and hydrogen isotopes suggest deposition from metamorphic fluids (calculated 61SOmo approximately +8 to + 13%o, measured range of 6D -52.2 to -27.3%0 ). Immiscible CO2-bearing fluids were trapped in the temperature range 280-350 °C with fluid pressure < ca. 600 bar. The inferred pressure-temperature history is attributed to late-metamorphic uplift, with fluid pressures falling below lithostatic. The sulphide-bearing veins are interpreted as a small-scale example of redistribution of mineral deposits by metamorphic fluids. Polymetallische Erzg/inge ("major veins") des westlichen Carbery Distriktes (County Cork) werden mit kleineren Gfingchen ("minor veins"), die in den benachbarten, eine disseminierte stratiforme Cu-Vererzung fiihrenden, Metasedimenten liegen, verglichen. Diese stratiformen Lagerst/itten sind an nichtmarine devonische Sedimente (Old Red Sandstone), die w/ihrend der hercynischen Orogenese metamorphisiert wurden, gebunden. Die Zusammensetzung der Schwefelisotope (634S) der Sulfide in der disseminierten Vererzung und in den kleineren G/ingen variiert yon -21.00 bis +5.14~o. Diese Zusammensetzung ist mit der Interpretation, dab der Schwefel in den G/ingchen aus den stratiformen disseminierten Sulfiden remobilisiert wurde, die ihrerseits diagenetischbakteriogene Signatur zeigen, konsistent. Die cg~S-Werte der Sulfate (Baryt) in den G/ingchen variieren yon + 12.3 bis + 15.7~oo, was mit einer Herkunft aus Grundw/issern iibereinstimmt. Die Homogenisierungs-Temperaturen der Fliil3igkeitseinschliisse in Quarz der G/ingchen sind mit einem EinschluB der Fluide w/ihrend des H6hepunktes der Metamorphose (300-400 °C, 1-3 kbar) konsistent. In den polymetallischen Erzg/ingen weisen die c~34S-Werte (-15.8 bis -4.2~o) auf die Remobilisation diagenetischen Schwefels, die Sauerstoff-und Wasserstoffisotope anf Ausffillung aus metamorphen Wiissern bin. Die berechneten 6*~O-Werte 1iegen zwischen ca. + 8 bis + 13%o, die gemessenen 6H-Werte zwischen -52.2 bis -27.3~o. Nicht mischbare CO24iihrende Fluide wurden im Temperaturbereich von 280-350 °C bei Fiuid-Drucken <ca. 600bar eingeschlossen. Der abgeleitete P-T Pfad wird mit sp/itmetamorpher Hebung, wiihrend der der Fluiddruck unter den lithostatischen Druck fiel, erkl/irt. Die Sulfid-ftihrenden G/inge werden als kleinmagst/ibliche Beispiele fiir Wiederverteilung yon Minerallagerst~itten durch metamorphe Fluide gedeutet.
Journal of the Geological Society, 1989
The Caledonian mafic and ultramfic intrusions of the Grampian region of northeast Scotland are sy... more The Caledonian mafic and ultramfic intrusions of the Grampian region of northeast Scotland are synorogenic tholeiitic plutons of middle Ordovician age. They include layered cumulates and xenolithic, contaminated and granular gabbroic varieties. The structurally complex Huntly–Knock intrusions contain locally significant quantities of Fe–Ni–Cu sulphide, while the associated country rock metasediments are sporadically enriched in Fe-sulphide. Sulphur isotope analyses on sulphide from within and around the intrusions give the following ranges of δ34S; – 0.1 to —1.7‰ for disseminated to massive sulphides in the complex and deformed Littlemill-Auchencrieve contact zone; +0.7 to +4.3‰ for disseminated interstitial sulphides within cumulate and granular rocks; + 1.7 to +6.0‰ for graphitic and sulphidic pyroxenitic pegmatites; –6.0 to +16.5‰ for disseminated sulphide from country rock metasediments; –4.0 to +8.2‰ for sulphides in partially melted sediments. δ34S of sulphides in the igneous rocks (χ̄ = +0.5 ± 2.4‰ (1σ), n = 36) lie within the range usually indicated for primary magmatic sulphur, i.e. 0 ±3‰, so that the sulphide system was probably dominated by magmatic sulphur. There is, however, a distinct difference between the isotopically heavier cumulate and granular rocks ( =±2.4 ± 1.2‰ (1σ) n = 9) and the lighter sulphide of the contact zone (χ̄ = –1.1 ± 0.4‰ (lσ), n = 21). The possibility that the slightly negative δ34S values of the contact zone are due to a contribution of 32S rich sulphur from sulphidic calcareous units is considered unlikely, due to the homogeneity of the contact zone δ34S values, and so the variation between the two groups is attributed to processes operative within the magma. Locally, an input from country rock sulphur has occurred as suggested by the δ34S values for xenolithic gabbro (+6.5‰), some of the graphitic and sulphidic pyroxenitic pegmatites (+5.9, +6.0‰) and possibly a basal olivine cumulate (+4.3‰). Although the data from the Littlemill-Auchencrieve contact zone are isotopically distinct from those Ni-Cu deposits dominated by crustal sulphur, petrographic evidence suggests that crustal involvement may have been important in the siting of the ore.
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Papers by Anthony Fallick