Gênese das mineralizações associadas ao magmatismo ácido na região do Garimpo do Papagaio, noroeste da Província Aurífera de Alta Floresta (MT)
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The Alta Floresta Gold Province is situated on the southern portion of Amazonian Craton and forms an elongate region with WNW-ESSE direction where auriferous deposits are associated with Paleoproterozoic plutonovolcanic magmatism.The area of research covers the Papagaio artisanal gold mining, located in Paranaíta, Mato Grosso.During geological mapping, plutonic to subvolcanic rocks bodies of granodioritic and granitic compositions were identified, as well as dacitic and rhyolitic volcanic and pyroclastic rocks.These lithotypes belong to the calc-alkaline series of medium to high potassium, meta-to peraluminous corresponding to type I granites of volcanic arc in an active continental margin.U-Pb ages showed that magmatism in the region has crystallized in the range of 1.80-1.78Ga with inherited zircons up to 2.1 Ga, showing evidence of a deeper and older crust during subduction.εNd (t) data showed the contribution of crustal and mantle material in the source with T DM age between 2.15-2.02Ga.These data revealed that volcanism in the area belongs to the Colíder Suite, corresponding to a magmatism that was active for approximately 16 Ma and evolved from dacitic to a rhyolitic composition.The mining prospect occurs on gold mineralization with copper, zinc and low levels of lead, preferably confined in veins that cut potassic, seritic and propylitic alteration halos.The existing veins in the region evolve systematically into six types: (I) Barren quartz vein associated with potassic alteration halo; (II) Quartz vein with ore minerals, sometimes associated with sericitic halo; (III) Sulphide vein with a well developed sericitic alteration halo in the salbands; (IV) and (V) Late quartz and carbonate veins; (VI) system of quartz veins newer and unrelated to deposit evolution.The first three types are similar to A-B-D system described in porphyry deposits, while the newer ones have characteristics of a shallower and epithermal environment.Gold occurs mainly in the central zone of the type II veins, in paragenesis with chalcopyrite + sphalerite + pyrite ± galena ± magnetite.The quartz of the veins underwent different intensities of recrystallization due to subsequent hydrothermal pulses and cathodoluminescence images showed that aquocarbonic fluid inclusions represent primary fluids with important participation in metalliferous content transportation.The results of D, O and S stable isotope in hydrothermal quartz, sericite and pyrite show that fluids are magmatic with meteoric contributions.In this context, the Papagaio artisanal mining developed on a continental magmatic arc, from the intrusion of hydrated and oxidized granite bodies that mark the final magmatic event of the Colíder Suite.It represents a porphyry deposit that was superimposed by epithermal intermediate-sulfidation characteristics as a result of hydrothermal telescoping, resulting from the lowering of the magma chamber.Keywords:
Metallogeny
<p>Cratons are representative of the oldest cores of continental crusts. Study of cratons is important &#160;as they preserve the pristine nature of continental crusts as well as they have economic significance as a major source of the world's mineral deposits. The crustal thickness, crustal composition, structure and physical properties of crust-mantle transition (the Moho) are the key parameters for understanding the formation and evolution of continental crust. The ratio of &#160;seismic P-wave and S-wave velocity (Vp/Vs) is used as a parameter to understand the petrologic nature of the Earth's crust. Using these parameters, we address the crustal properties of all Archean cratons. The teleseismic P-wave receiver function analysis reveals that all the Eoarchean (4-3.6 Ga) cratons (Superior, North Atlantic Craton, North China Craton, Yilgarn, Zimbabwe, Kaapvaal) have crustal thickness ranges between 34-42 km and Vp/Vs ratio 1.68-1.79, the Paleoarchean (3.6-3.2 Ga) cratons (Baltic shield, Pilbara, Tanzania, Grunehogna) have 29-52 km crustal thickness and Vp/Vs ratio 1.7-1.85, the Mesoarchean (3.2-2.8 Ga) cratons (Sao Francisco, Guapore, Yangtze, Antananarivo) have 36-53 km thickness and Vp/Vs ratio 1.7-1.9, and Neoarchean (2.8-2.5 Ga) cratons (Guiana, Anabar, Gawler, Napier, Tarim) have 36-59 km thickness and Vp/Vs ratio 1.64-1.95. The nature of crust-mantle transition is overall sharp and flat. &#160;We also found that the crusts which are stabilized earlier, are thinner compared to the later stabilized crusts. Our findings are well-correlated with the craton evolution process predicted by Durrheim and Mooney (1994), where older crusts are thin due to delamination process and relatively younger crusts are thick due to basaltic underplating. Our result of higher Vp/Vs ratio in the relatively younger crusts corroborates with the mafic nature of the crust whereas the older crusts are felsic-intermediate resulting lower Vp/Vs ratio. Our study is unique as it includes most of the global cratons and suggests a global model of continental crust formation and evolution process.</p>
Receiver function
Baltic Shield
Yilgarn Craton
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The outstanding questions is how to quantitatively estimate the rate of growth of the continental crust and the proportion of juvenile material added to the crust at any given time during its evolution. In recent years, the U-Pb and Hf isotopic composition of detrital zircons provide an effective and simple approach to constrain the periods and rate of continental growth. In order to characterize the crustal growth history of North China Craton, 187 detrital zircons in two sand samples from the lower reach of Jing River and the Luo River were measured for Lu-Hf isotopic compositions by LA-MC-ICPMS. Compared with the global continental crust, the North China Craton shows a characteristic of episodic continental growth rate. For instance, about 60% of the present crustal volume of the North China Craton was generated in the between Mesoarchean and Late Neoarchean (3.0 to 2.5Ga). Since then, the continental crust keeps a stable rate of growth and completely formed at the end of the Neoproterozoic (600Ma). It indicates that the present crustal of the North China Craton was mainly growth during Archean and Proterozoic, and the juvenile additions to the continental crust are almost negligible during Phanerozoic. Combined with the available studies and the early Precambrian crust growth curves of based on U-Pb ages, two-stage Hf crust formation ages(tDM2C and tNC2C)and eHf(t), our results also reveal that ～2.7Ga and ～2.5Ga are the most prominent time of magmatism and the period of continental rapidly growth, respectively. Indicating that the North China Craton has been experienced obviously twice crustal growth.
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This paper gives an overview of the basic features of the structure and composition of the continental crust in East China.It summarizes the destruction of the North China Craton and its mechanisms,the hot topic for geodynamic community in the literature.By comparing different rheological structures of continental lithosphere,the significance of rheological properties of continental lower crust is emphasized for understanding the destruction mechanism of the North China Craton.It is suggested that fine rheological experiments at high pressure and temperature and quantitative hydroxyl analyses are important for solving the destruction mechanism puzzle.
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