Multi-Stage Formation of Apatite in the Early Proterozoic Metagabbroids of the Velimyaki Massif (the Northern Ladoga Region)

The paper considers the petrographic composition of the Mesozoic alkaline igneous rocks of the Yukhta massif. It is part of the Central Aldan ore region and is spatially located in the central part of the Nymnyr block. The massif is a large multiphase structure, of the most productive stage of the territory’s development – the Mesozoic tectonic-magmatic activation of the Aldan-Stanovoy shield. Determination of the qualitative quantitative-mineralogical characteristics of the 2 and 3 phases of intrusion (emplacement) most promising for gold-radioactive mineralization with the help of crystal-optical methods was the main goal of this work. As a result of petrographic studies of Mesozoic alkaline igneous rocks, it is defined that, the Yukhta massif is a multiphase magmatic structure, with decrease of the content of dark-colored minerals in rocks from the early to later phases of intrusion. In general, the rocks of the massif bear significant traces of secondary changes, which are related to the gradual formation of the massif. According to the features of the composition of the massif rocks, it was found that the latter could be formed from residual differentiates during the fractional crystallization of rock-forming minerals with the involvement of plagioclases. The Yukhta massif is associated with the large Samolazovskoye gold deposit, which formation is related to an intense contact-metasomatic impact on carbonate rocks. Hydrothermal-metasomatic transformations of the latter are the products of multi-stage silica-alkaline metasomatosis associated with the second and especially with the third phases of the massif intrusion, and with further weathering processes, involving karst formation, disintegration of gold-ore metasomatites and the formation of a thick oxidation zone. From whence it is concluded that uranium being a chemically active element does not accumulate in a hypergenic form within the Yukhta massif. Where the weathering crust is intensively developed, a gold-ore type of mineralization is observed. On the other hand, the rocks of the massif itself, in particular syenites of the 2 and 3 phases of intrusion, may be promising for the uranium-thorium-rare earth (U-Tn-REE) type of mineralization. In general, these studies in this direction will provide insight into a number of issues related to the study of the evolution and metallogeny of the Mesozoic tectonic-magmatic activation of the Aldan-Stanovoy Shield

Detrital zircon ages from quartzite and metaconglomerate in the Tusas and Picuris Mountains in northern New Mexico reveal new information about age and provenance trends within a >1000 km 2 Proterozoic sedimentary basin and provide a critical test of regional correlations. Samples from the Paleoproterozoic Vadito and Hondo groups are dominated by a single detrital zircon population with age probability peaks that range from 1765 to 1704 Ma. Minor Archean and ca. 1850 Ma age probability peaks were also recognized in some samples. Close correspondence between detrital zircon ages and the age of surrounding basement rocks indicates predominately local sources, and we interpret systematic shifts in peak ages with stratigraphic position to represent changes in local sources through time. Similarities of age spectra support previous correlation of stratigraphic units between discontinuous exposures of the Hondo Group. We interpret that these supracrustal rocks were deposited in a single basin that we refer to as the Pilar basin. Two samples of the Marquenas Formation, a pebble to boulder conglomerate previously correlated with the ca. 1700 Ma Vadito Group, are dominated by Paleoproterozoic detrital zircon with age probability peaks at 1707 and 1715 Ma in the middle and upper units, respectively. Unlike the Vadito and Hondo group samples, the Marquenas Formation also contains abundant ca. 1700–1600 Ma zircon derived from Mazatzal-aged sources to the south and Mesoproterozoic zircon with age probability peaks at 1479 and 1457 Ma. Weighted averages of 1477 ± 13 Ma and 1453 ± 10 Ma for the youngest detrital zircon in the middle and upper Marquenas Formation provide new maximum depositional age constraints, indicating that it is not part of the Vadito Group. The minimum age is not well constrained but is interpreted to be ca. 1435 Ma on the basis of the timing of regional metamorphism and deformation previously documented in the Picuris Mountains. These data represent the first evidence of sedimentation directly associated with ca. 1.4 Ga regional metamorphism, plutonism, and deformation in the southwestern United States and provide an important new constraint on the tectonic evolution of southern Laurentia during this time.

Geochronology and geochemistry of metamorphic rocks in the Jiaobei terrane: Constraints on its tectonic affinity in the Sulu orogen

The Inyoni shear zone represents an important tectonic boundary between (i) the ca. 3.45 Ga high-pressure amphibolite facies, granite-greenstone domain south of the Barberton greenstone belt, termed the Stolzburg terrane, and (ii) the ca. 3.29 to 3.23 Ga rocks of the trondhjemitic Badplaas pluton to the west. The Stolzburg terrane is separated from the greenschist facies rocks of the rest of the Barberton greenstone belt by the Komati fault, which records >10 km uplift of the Stolzburg terrane relative to the lower-grade rocks of the greenstone belt at ca. 3.23 Ga. A number of studies within the Stolzburg terrane have documented high-pressure amphibolite facies metamorphism that occurred concurrently with exhumation, with the lowest apparent geothermal gradients documented in the Inyoni shear zone, where strong constraints on the age of metamorphism are most limited. In addition, different studies on Inyoni metamorphism have produced significantly different temperature estimates. This study utilizes garnet Sm-Nd geochronology in combination with P-T modelling to directly date the metamorphism and re-evaluate the P-T conditions of the Inyoni shear zone. Two petrologically distinct samples produce similar P-T evolutions. A heterogeneous sample with both garnet-bearing and garnet-absent domains gives up-P evolutions reaching conditions of 550 to 675°C and 7 to 10 kbar, whereas a homogenous sample containing garnet and clinopyroxene produces a similar dominantly up-P evolution reaching peak conditions of 650°C and 8 to 10 kbar. Sm-Nd garnet ages of 3 201.6 ± 4.7 Ma (MSWD = 1.02) and 3 200.3 ± 5.3 Ma (MSWD = 0.44) were obtained from two samples of the homogenous garnet and clinopyroxene-bearing amphibolite. The Sm-Nd garnet geochronology provides accurate ages for the metamorphism of the Inyoni shear zone, with age results suggesting activity on the Inyoni shear zone may have continued after the regional metamorphism at ca. 3.23 Ga previously established by zircon U-Pb geochronology. However, 147Sm decay constant uncertainty leaves open the possibility that Inyoni garnet growth could have coincided with the previously recognized 3.23 Ga regional metamorphism.

Ageological transect across volcano-sedimentary extensions of the southeastern margin of the Wakeham Group (eastern Grenville Province) and surrounding granitoid rocks has revealed the existence of polyphase Pinwarian (ca. 1.5 Ga) and Grenvillian (1.01 Ga) deformation and regional metamorphism. Metamorphic grade in the 1.5 Ga Wakeham Group extensions increases to the southeast from middle amphibolite to granulite facies, whereas the gneissic granitoid rocks record 1.01 Ga regional metamorphism that reached middle amphibolite facies. We suggest that a compartmentalization of Grenvillian deformation on a regional scale, with deformation effects concentrated in zones of less competent material, led to the preservation of the early granulites. On a regional scale, the pattern defined by the Grenvillian fabric within the granitoids and metasedimentary rocks consists of basin-and-dome structures produced by polyphase tectonics.

The southeast Reynolds Range, central Australia, is cut by steep northwest‐trending shear zones that are up to hundreds of metres wide and several kilometres long. Amphibolite‐facies shear zones cut metapelites, while greenschist‐facies shear zones cut metagranites. Rb–Sr and 40Ar–39Ar data suggest that both sets of shear zones formed in the 400–300 Ma Alice Springs Orogeny, with the sheared granites yielding well‐constrained 40Ar–39Ar ages of ca 334 Ma. These data imply that the shear zones represent a distinct tectonic episode in this terrain, and were not formed during cooling from the ca 1.6 Ga regional metamorphism. A general correlation between regional metamorphic grade and the grade of Alice Springs structures implies a similar distribution of heat sources for the two events. This may be most consistent with both phases of metamorphism being caused by the burial of anomalously radiogenic heat‐producing granites. The sheared rocks commonly have undergone metasomatism implying that the shear zones were conduits of fluid flow during Alice Springs times.

Multi-stage Cu remobilization of the Huping metamorphic-hydrothermal deposit in the southern North China Craton

Skarn deposits are found on every continents and were formed at different times from Precambrian to Tertiary. Typically, the formation of a skarn is induced by a granitic intrusion in carbonates-rich sedimentary rocks. During contact metamorphism, fluids derived from the granite interact with the sedimentary host rocks, which results in the formation of calc-silicate minerals at the expense of carbonates. Those newly formed minerals generally develop in a metamorphic zoned aureole with garnet in the proximal and pyroxene in the distal zone. Ore elements contained in magmatic fluids are precipitated due to the change in fluid composition. The temperature decrease of the entire system, due to the cooling of magmatic fluids and the entering of meteoric water, allows retrogression of some prograde minerals. The Hammerlein skarn deposit has a multi-stage history with a skarn formation during regional metamorphism and a retrogression of primary skarn minerals during the granitic intrusion. Tin was mobilized during both events. The 340 Ma old tin-bearing skarn minerals show that tin was present in sediments before the granite intrusion, and that the first Sn enrichment occurred during the skarn formation by regional metamorphism fluids. In a second step at ca. 320 Ma, tin-bearing fluids were produced with the intrusion of the Eibenstock granite. Tin, which has been added by the granite and remobilized from skarn calc-silicates, precipitated as cassiterite. Compared to clay or marl, the skarn is enriched in Sn, W, In, Zn, and Cu. These metals have been supplied during both regional metamorphism and granite emplacement. In addition, the several isotopic and chemical data of skarn samples show that the granite selectively added elements such as Sn, and that there was no visible granitic contribution to the sedimentary signature of the skarn The example of Hammerlein shows that it is possible to form a tin-rich skarn without associated granite when tin has already been transported from tin-bearing sediments during regional metamorphism by aqueous metamorphic fluids. These skarns are economically not interesting if tin is only contained in the skarn minerals. Later alteration of the skarn (the heat and fluid source is not necessarily a granite), however, can lead to the formation of secondary cassiterite (SnO2), with which the skarn can become economically highly interesting.

Although less common than hematite ores, high-grade magnetite ores represent a distinct type of iron mineralization hosted by banded iron formations (BIFs). The Gongchangling iron deposit hosted in ~2.55 Ga BIFs in the North China craton represents one of the most economically important iron deposits in China. Located in mining area II, it is a high-grade (>50 wt % Fe) magnetite deposit and one of the largest of its type in the world. However, the lack of reliable age constraints on iron mineralization has hindered the testing of competing genetic models for the formation of the Gongchangling deposit. In situ U-Pb geochronology of monazite and zircon intergrown with garnet from the proximal alteration zone of a high-grade iron orebody yielded an age of 1.86 Ga, which represents the timing of formation of high-grade magnetite mineralization. This age is coeval with a tectonic extension event recorded in the northeastern North China craton. Our results preclude the previously suggested genetic link between high-grade magnetite mineralization and ~2.50 Ga regional metamorphism. Growth of authigenic monazite and zircon is likely related to the breakdown of detrital zircon, which has undergone metamictization. In combination with previously published data, we propose that the development of zoned alteration associated with the deposit, which is characterized by the garnet-amphibole-magnetite assemblage in the proximal zone changing to a chlorite-quartz–dominated assemblage in the distal zone, can be attributed to a gradual decrease in temperature from >550° to ~250°C and to alteration minerals forming from leaching of the BIFs instead of by replacement of the wall rocks. Magnetite mineralization was controlled by the well-developed faults that cut the BIFs and provided conduits for silica-undersaturated alkaline meteoric fluids. Fluid flow likely took place in an extensional tectonic regime, similar to that invoked elsewhere for hematite mineralization but at greater depths.

The article states new views on structural features of East Orenburg Oblast. Results of long-term research of geological party of Mineral Deposits and their Investigation Department in RUDN formed the basis of writing the article. Unlike the predecessors considering this territory as a fragment of a double-fold structure of Ural, the authors of the article realize the thought of paleovolcanic structure of the territory. Having carried out photointerpretation of multiband satellite images, the scheme of tectonic disturbances, which is a combination of ring and radial faults, has been received. These disturbances emphasize the large ring structure, the center of which settles down near the Zhetykol lake. The carried-out facies analysis of volcanogenic and sedimentary rocks showed that groups of rocks corresponding to the main facies of volcanic constructions - vent, slope and distal - are outstanding for the territory. Rocks of these facies were formed in two independent tectono-magmatic cycles: the Baikal - Ordovician-Silurian age, and Caledonian - Upper Devonian-Upper Carboniferous age. The magmatism sequence is homodromous in both cycles and particular intrusive facies correspond to each cycle. For the Baikal cycle the intrusions are presented by serpentinite and ultramafite. For the Caledonian cycle the intrusive rocks are presented by complex granitoid intrusions of three-facies composition (the initial stages of intrusion are presented by gabbro and gabbro-diorites, the second phase of intrusion - by diorites, syenites and granodiorites, the third phase - by various granites). Interaction of granitoids with serpentinite leads to remobilization of dunite from serpentinite and to formation of chromite industrial mineralization in the latter. The research results open new opportunities in the analysis of allocation and confinedness of the known endogenous ore objects and predicting the new.

Skarn formation and tin enrichment during regional metamorphism: The Hämmerlein polymetallic skarn deposit

The thesis area contains metasediments of the Neranleigh-Fernvale regional metamorphics, Upper Permian rhyolitic and andesitic lavas, volcaniclastics and dykes, and a Lower Triassic pluton.The metasediments, consisting of phyllites, cherts and siliceous mudstones, were originally deposited during the Devonian to Lower Carboniferous. In the study area the regional metamorphism, in the Upper Carboniferous, reached the prehnite-pumpellyte facies.The extrusive sequence of the Brookfield Volcanics begins with rhyolitic lavas and pyroclastics. The overlying andesitic rocks consist of a basal pyroclastic layer, followed by voluminous quantities of thinly interbedded flows and volcaniclastics. A minor, late rhyolitic phase brought this extrusive phase to a close. Several rhyolite and andesite dykes, contemporaneous with extrusion, were also noted. Chemically, the volcanics are high-K calcalkaline rocks extruded at a late stage in the geological evolution of Southeast Queensland. 500 million m3 of high grade aggregate is a conservative estimate for the reserves of the extrusives.The Kholo Creek Quartz Diorite pluton consists of various intrusive phases dominated by low-Si, moderate-K, calcalkaline diorites. A source from the mantle derived by partial melting is postulated for the pluton; and magmatic stoping, at a depth of less than 8km below the surface, is the most favoured mechanism of emplacement. When the first phase crystallised low PH20 conditions prevailed; but, as crystallisation proceeded, the PH20 increased and the bulk composition changed from quartz gabbro through to aplite. The contact aureole extends for no more than 120 metres from the contact. The reserves of this intrusive phase can be estimated at 300 million m3 .Field observations, laboratory test results and petrological information of the various rock units indicate that the area could provide Brisbane and Ipswich with crushed rock, for a variety of purposes, for many years. Based on the demand in the year 2000 calculated by A.A. Heat>) and Partners (1978), quarrying operations could continue for at least 100 years.

Two granite-granodiorite-tonalite-trondhjemite (TTG) complexes intruded mafic-intermediate volcanic and volcaniclastic rocks at 1954-1940 Ma in the central part of the Knaften area, which lies in the northern part of the Palaeoproterozoic Bothnian Basin, in the central part of the Fennoscandian Shield, northern Sweden. The regional metamorphism was upper greenschist to amphibolite facies. The granitoid complexes are subdivided texturally into three types of intrusions. Contact relationships show that the most coarse-grained type is the oldest, followed by a medium-grained type and finally an aplitic-pegmatitic type intrusion. Felsic dykes that cut the granitoids form the youngest intrusive event. Myrmekitic/symplectitic textures or graphic intergrowths show that the later intrusive phases were more volatile-rich. The granitoids are high-level intrusions, and formed the root-zone of a volcano. Close to, but outside the granitoid complexes, compositionally similar felsic porphyry dykes occur. A package of reworked felsic tuffaceous rocks occurs in the northern part of the Knaften area and may constitute extrusive equivalents of the intrusions. These clastic rocks display primary structures such as cross bedding, which indicate deposition in shallow water. Geochemically, the Knaften intrusions are granites, granodiorites, tonalites and trondhjemites. The northern granitoids are more fractionated than the southern ones, and some felsic dykes are geochemically similar to the southern intrusions. The tuffaceous rocks are intermediate in composition between the felsic and more mafic intrusive phases. All Knaften felsic phases have similar trace element patterns and, their trace element chemistry is similar to other rocks from collisional settings in island arc terrains.

The Aitik Cu-Au-Ag deposit in northern Sweden is hosted by strongly altered and deformed 1.9 Ga old Svecofennian volcaniclastic rocks. A porphyritic quartz monzodiorite intrusion of subvolcanic origin is situated in the structural footwall to the ore. U–Pb TIMS zircon dating of the quartz monzodiorite yielded an age of 1887±8 Ma, which coincides with the age obtained for the subduction-related Haparanda suite of granitoids in Norrbotten. It is intruded by minor, comagmatic phases, including units of finer grained quartz monzodiorite and diorite. The finer grained intrusive phase, which can be traced into the ore zone of the Aitik deposit, is believed to represent apophyses protruding from the upper part of the quartz monzodiorite. The Aitik intrusion, comprising the quartz monzodiorite and its comagmatic phases, is affected by regional metamorphism, deformation, and hydrothermal alteration. Potassic alteration is most evident, and expressed by the growth of secondary biotite and K-feldspar. The sub-economic Cu-Au-Ag mineralization hosted by the Aitik intrusion mainly consists of chalcopyrite, pyrite, and magnetite of dominantly magmatic-hydrothermal origin, and is present in four forms: disseminated, as veinlets, in quartz-feldspar veins, and in biotite-amphibole veins. This mineralization extends in economic grades into the adjacent volcaniclastic rocks in the roof of the intrusion. The Aitik intrusion is similar in many respects to porphyry copper generating intrusions regarding tectonic setting, petrography and chemical composition. The intrusion-hosted sub-economic mineralization might form part of a porphyry system with its major part represented by the main mineralization in the overlying volcaniclastic rocks.

The massif of Fedorov Tundra was formed as part of the Paleoproterozoic (2.5 Ga) Fedorov-Pana platinum-bearing layered complex as a result of consecutive emplacement of two intrusive phases. The emplacement of the first phase resulted in the formation of a large layered intrusive body composed of amphibole gabbro, gabbronorite, norite, pyroxenite, olivine pyroxenite, and harzburgite. The second phase gave birth to a gabbronorite intrusion smaller in volume and enriched in sulfides and PGM. Magmatic breccia has been observed in the contact zone between two phases. The rocks of the massif are referred to the series of normal alkalinity and to the quartz- and olivine-normative groups differing in saturation with silica. Using isoplethic and isobaric joins of the q-fo-fa-di-hd-ab-an-aq phase diagram, the stages of rock formation are considered. The thermodynamic conditions of rock crystallization were determined as T = 1000−800°C and \( P_{H_2 O} \) = 1000−2500 bar for the first intrusive phase and T = 1000–900°C and \( P_{H_2 O} \) = 800−1000 bar for the second intrusive phase.