Dissolution of Pyrochlore and Microlite in Alkaline,Subaluminous, and Peraluminous Granitoid Melts

Doklady Earth Sciences - The data of experiments are presented on the Ta and Nb concentrations in acidic magma melts of various compositions upon dissolution of pyrochlore and microlite at...     

金在花岗质熔体中溶解度的初步实验研究

以合成花岗岩、水、不同浓度的盐酸溶液、氢氟酸溶液作为反应初始物,在850℃,100 MPa,接近于NNO的条件下开展了金在不同花岗质熔体中溶解度的实验研究,实验固液相产物中的金含量使用石墨炉原子吸收法测定。实验结果显示,金在花岗质熔体中的溶解度变化范围为1.87～156.62μg/g,流体相中金的溶解度为0.31～6.92μg/g;金在熔体相中的溶解度较其在共存液相中的高。花岗质熔体相中金的溶解度明显受熔体化学组成的影响,过碱性富钠花岗质熔体中金的溶解度明显高些;金在花岗质熔体中的溶解度随着熔体中Na2O/K2O摩尔比增大而增大;在氟氯共存岩浆体系中,氟含量变化对金在熔体相中的溶解度影响不明显,而液相中氯含量增大有利于提高金在流体相中的含量。     

The Solubility of Sulphur in Hydrous Rhyolitic Melts

Experiments performed at 2 kbar, in the temperature range 800–1000°C,with fO₂ between NNO–2·3 and NNO+2·9 (whereNNO is the nickel–nickel oxide buffer), and varying amountsof sulphur added to hydrous metaluminous rhyolite bulk compositions,were used to constrain the solubility of sulphur in rhyolitemelts. The results show that fS₂ exerts a dominant control onthe sulphur solubility in hydrous silicate melts and that, dependingon fO₂, a rhyolitic melt can reach sulphur contents close to1000 ppm at high fS₂. At fO₂ below NNO+1, the addition of ironto a sulphur-bearing rhyolite magma produces massive crystallizationof pyrrhotite and does not enhance the sulphur solubility ofthe melt. For a given fO₂, the melt-sulphur-content increaseswith fS₂. For fixed fO₂ and fS₂, temperature exerts a positivecontrol on sulphur solubilities, at least for fO₂ below NNO+1.The mole fraction of dissolved sulphur exhibits essentiallylinear dependence on fH₂S at low fO₂ and, although the experimentalevidence is less clear, on fSO₂ at high fO₂. The minimum insulphur solubility corresponds to the redox range where bothfH₂S and fSO₂ are approximately equal. A thermodynamic modelof sulphur solubility in hydrous rhyolite melts is derived assumingthat total dissolved sulphur results from the additive effectsof H₂S and SO₂ dissolution reactions. The model reproduces wellthe minimum of sulphur solubility at around NNO+1, in additionto the variation of the sulphide to sulphate ratio with fO₂.A simple empirical model of sulphur solubility in rhyoliticmelts is derived, and shows good correspondence between modeland observations for high-silica rhyolites. KEY WORDS: sulphur; solubility; rhyolite; thermodynamics; fO₂; fS₂     

Crystallization of Chromite and Chromium Solubility in Basaltic Melts

The equilibrium between chromite and melt has been determinedon four basalts at temperatures of 1200–1400?C over arange of oxygen fugacity (f_o2) and pressures of 1 atm and 10kb. The Cr content of chromite-saturated melts at 1300?C and1 atm ranges from 0?05 wt.% Cr₂O₃ at a log f_o2= –3 to1?4 wt.% at a log f_o2=–12?8. The Cr²⁺/Cr³⁺ of melt increaseswith decreasing f_o2 and is estimated by assuming a constantpartitioning of Cr³⁺ between chromite and melt at constant temperature.The estimated values of Cr²⁺/Cr³⁺ in the melt are at f_o2 valuesof 4–5 orders of magnitude lower than the equivalent Fe²⁺/Fe³⁺values. The Cr/(Cr+Al) of chromite coexisting with melt at constanttemperature changes little with variation of f_o2 below log f_o2=–6.Five experiments at 10 kb indicate that Cr₂O₃ dissolved in themelt is slightly higher and the Cr/(Cr + Al) of coexisting chromiteis slightly lower than experiments at 1 atm pressure. Thus variationin total pressure cannot explain the large variations of Cr/(Cr+ Al) that are common to mid-ocean ridge basalt (MORB) chromite. Experiments on a MORB at 1 atm at f_o2 values close to fayalite-magnetite-quartz(FMQ) buffer showed that the Al₂O₃ content of melt is highlysensitive to the crystallization or melting of plagioclase,and consequently coexisting chromite shows a large change inCr/(Cr + Al). It would appear, therefore, that mixing of a MORBmagma containing plagioclase with a hotter MORB magma undersaturatedin plagioclase may give rise to the large range of Cr/(Cr +Al) observed in some MORB chromite.     

Experimental Study of Sulfur Solubility in Silicate Melts Coexisting with Graphite as a Function of Silicate Melt Composition

Abstract. Sulfur (S) solubility is determined in silicate melts, in particular with low-FeO content coexisting with graphite. In a high FeO range (>10 mol %), the S solubility is strongly dependent on the FeO content in silicate melt, which is in good agreement with previous works. In an intermediate FeO range (1∼10 mol %), the S solubility in melts with a multi-component system is higher than that in melts with a simple system. The SKα shift of the electron microprobe shows the dissolve sulfur is all sulfide. A positive dependence is observed between CaO and S content in the melt undoped with FeO, but the dissolved sulfur is sulfate. The relationship between melt composition, S content, and S oxidation state is discussed.     

Partitioning of Nb,Ta, Ti,Ce, and La between Granitoid Magmatic Melts and Minerals

Doklady Earth Sciences - Experimental data on the Nb, Ta, Ti, Ce, and La concentrations in felsic magmatic melts of various alkalinity and alumina content upon dissolving ilmenorutile,...     

Sediment Melts at Sub-arc Depths: an Experimental Study

The phase and melting relations in subducted pelites have beeninvestigated experimentally at conditions relevant for slabsat sub-arc depths (T = 600–1050°C, P = 2·5–4·5GPa). The fluid-present experiments produced a dominant paragenesisconsisting of garnet–phengite–clinopyroxene–coesite–kyanitethat coexists with a fluid phase at run conditions. Garnet containsdetectable amounts of Na₂O (up to 0·5 wt%), P₂O₅ (upto 0·56 wt%), and TiO₂ (up to 0·9 wt%) in allexperiments. Phengite is stable up to 1000°C at 4·5GPa and is characterized by high TiO₂ contents of up to 2 wt%.The solidus has been determined at 700°C, 2·5 GPaand is situated between 700 and 750°C at 3·5 GPa.At 800°C, 4·5 GPa glass was present in the experiments,indicating that at such conditions a hydrous melt is stable.In contrast, at 700°C, 3·5 and 4·5 GPa, asolute-rich, non-quenchable aqueous fluid was present. Thisindicates that the solidus is steeply sloping in P–T space.Fluid-present (vapour undersaturated) partial melting of thepelites occurs according to a generalized reaction phengite+ omphacite + coesite + fluid = melt + garnet. The H₂O contentof the produced melt decreases with increasing temperature.The K₂O content of the melt is buffered by phengite and increaseswith increasing temperature from 2·5 to 10 wt%, whereasNa₂O decreases from 7 to 2·3 wt%. Hence, the melt compositionschange from trondhjemitic to granitic with increasing temperature.The K₂O/H₂O increases strongly as a function of temperatureand nature of the fluid phase. It is 0·0004–0·002in the aqueous fluid, and then increases gradually from about0·1 at 750–800°C to about 1 at 1000°C inthe hydrous melt. This provides evidence that hydrous meltsare needed for efficient extraction of K and other large ionlithophile elements from subducted sediments. Primitive subduction-relatedmagmas typically have K₂O/H₂O of 0·1–0·4,indicating that hydrous melts rather than aqueous fluids areresponsible for large ion lithophile element transfer in subductionzones and that top-slab temperatures at sub-arc depths are likelyto be 700–900°C. KEY WORDS: experimental petrology; pelite; subduction; UHP metamorphism; fluid; LILE     

Peralkalinity, Al{rightleftharpoons}Si Substitution, and Solubility Mechanisms of H2O in Aluminosilicate Melts

The solubility mechanisms of H₂O in peralkaline sodium aluminosilicatequenched melts (anhydrous NBO/T = 0.5) have been studied withRaman spectroscopy as a function of Al/(Al + Si) (0–0–3)and H²O content (0–7.5 wt.%). The coexisting structuralunits in the anhydrous quenched melts are TO2 (Q4), T2O5(Q3),and TO3 (Q2). In Al-free Na₂Si₄O₉ (NS4) melt, H₂O forms complexes with Na⁺(Na–OH bonds) and with Si⁴⁺ (Si–OH bonds). MolecularH₂O is also detected. TO3 structural units are not detectedin this composition. In the H₂O concentration range between0 and 4 wt.%, there is an approximately 20% increase in NBO/Tresulting from the increased abundance ratio, T₂O₅/TO2. Withfurther increments in water activity, the NBO/T of hydrous NS4melt is reduced. The depolymerization results from hydroxylationof the silica tetrahedra, whereas polymerization is due to formationof complexes with Na–OH bonding. In Al-bearing compositions on the Na₂Si₄O₉–Na₂(NaAl)₄O₉–join, there is evidence for Al–OH bonding in additionto Na–OH and Si–OH bonds. Among these complexes,the relative abundance of those with Si–OH bonds diminisheswith increasing Al/(A1 + Si), whereas complexes with Al–OHand Na–OH bonds become more important. Complexes withNa–OH bonds dominate for H₂O4 wt.%, whereas complexeswith Al–OH dominate at higher water content. The threestructural units, TO₃, T₂O₅, and TO², were observed in bothanhydrous and hydrous peralkaline sodium aluminosilicate melts.Their abundance varies, however, with the H₂O concentrationin the melts. The NBO/T decreases to a minimum (a 30–50%lowering of NBO/T relative to anhydrous materials) for low H₂Ocontents (3–4 wt.% H₂O), and increases as the H₂O contentis increased further.     

绿柱石与硅铍石原位结晶实验研究

绿柱石与硅铍石均为铍矿物家族中的主要成员,是重要的工业铍矿物,利用背散射和电子探针研究矿物特性时,常可见两者共生或发生交代的现象（饶灿,2009;Reyf, 2008; Evensen, 1999）,其结晶条件对于成矿环境与成矿机制均具有重要的指示意义。前人已进行了关于绿柱石,硅铍石等铍矿物稳定性的实验研究,但研究多采用高温淬火的高温高压实验装置,误差大,且无法原位观测矿物结晶习性（王振杰, 1992;Sirbescu et al., 2009）,本文利用热液金刚石压腔,原位观测了绿柱石与硅铍石的结晶过程,得到了它们结晶的温压条件及结晶习性。     

花岗质岩石的基本问题

当代地球科学的两个前缘领域一个是地球的早期历史，一个是地球的深部过程，这两个问题都与花岗质岩石紧密相关。花岗质岩石主要由石英、斜长石和碱性长石组成，并因此具有较低的密度。这种性质决定了花岗质岩石具有正的浮力，记录了很长的地球演化历史。因此，花岗岩类是地质学最复杂的话题之一，因为其源区岩石多种多样和形成过程非常复杂。本文的目的是帮助普通旅游者识别花岗质岩石及其重要意义。通常，花岗岩（狭义）被定义为由石英（〉20％，按体积计算）和长石（碱性长石大于斜长石）组成的深成岩。但是，地质学家常常将特征与花岗岩（狭义）类似的深成岩称为花岗质岩石或花岗岩类，也就是广义花岗岩。因此，花岗岩类是深成岩的一个大类，包括象花岗闪长岩、二长花岗岩、正长花岗岩、英云闪长岩等这样的岩石。火成岩的多样性不仅仅取决于岩浆作用过程，而且也取决于岩浆形成过程。岩浆的产生是源区岩石部分熔融的结果，因而火成岩的化学成分取决于源区成分、熔融温度和压力、挥发分以及熔融程度。尽管岩浆作用过程对火成岩的成分具有重要影响，花岗质岩石多样性的关键因素却是部分熔融作用。基于此，岩石学家更注意花岗质岩浆的起源而不是它们的演化。花岗质岩浆虽然起源于地壳，却是受地幔热引擎的驱动。因此，花岗质岩石也记录了大量地球深部过程的信息。     

Trace Elements in Alkaline Lamprophyres,Clinopyroxene, and Amphibole of the Tomtor Massif and the Ore Potential of the Melts

Data obtained on lamprophyres from the carbonatite–volcanic unit in the lower horizon of the Tomtor Massif indicate that the rocks and zoned diopside and kaersutite phenocrysts in them are enriched in incompatible elements more significantly than is typical of alkaline ultramafic rocks of the Maymecha–Kotui and Kola provinces. The concentrations of these elements and their indicator ratios in the cores and intermediate zones of the diopside and kaersutite phenocrysts significantly vary, and this suggests that the minerals might have crystallized from different melts. This is consistent with the earlier conclusions, which were derived from studying melt inclusions, that the phenocrysts crystallized from mixing alkaline mafic melts of sodic and potassic types and different Mg–number which were enriched in the carbonatite component. The cores of the diopside phenocrysts started to crystallize from sodic mafic magma in a magmatic chamber, while the intermediate and outermost zones of this mineral crystallized from mixed sodic–potassic mafic melts. The carbonatite component was separated from the sodic mafic melt at high temperature (>1150°C) during diopside core crystallization. The bulk compositions of the alkaline lamprophyres and of the diopside and kaersutite phenocrysts contain lower normalized concentrations of HREE than LREE. This led us to conclude that the parental sodic and potassic mafic melts were derived from an enriched mantle source material under garnet–facies parameters, as is typical of continental rifts. It is noteworthy that the potassic mafic melt was derived at greater depths and lower degrees of melting of the mantle source than the sodic melt. The iron–rich sodic melt from which the cores of the diopside phenocrysts started to crystallize was enriched in V, REE, Y, and volatile components (H₂O, CO₂, F, Cl, and S). The onset of carbonate–silicate liquid immiscibility was marked by the redistribution of REE and Y into the carbonatite melt. The potassic, more Mg–rich mafic melt from which the intermediate and outermost zones of the diopside phenocrysts crystallized was enriched in Ti, Nb, Zr, and REE and always remained homogeneous when this mineral crystallized.     

Evolution of Mafic Alkaline Melts Crystallized in the Uppermost Lithospheric Mantle: a Melt Inclusion Study of Olivine-Clinopyroxenite Xenoliths, Northern Hungary

Olivine-clinopyroxenite xenoliths exhumed in alkali basalts(sensu lato) in the Nógrád–GömörVolcanic Field (NGVF), northern Hungary, contain abundant silicatemelt inclusions. Geothermobarometric calculations indicate thatthese xenoliths crystallized as cumulates in the upper mantlenear the Moho. These cumulate xenoliths are considered to representa period of Moho underplating by mafic alkaline magmas priorto the onset of Late Tertiary alkaline volcanism in the Carpathian–Pannonianregion. The major and trace element compositions of silicatemelt inclusions in olivine display an evolutionary trend characterizedby a strong decrease in CaO/Al₂O₃. The parental melt of thecumulates was a basanite formed by low-degree ( 2%) partialmelting of a garnet peridotite source. The compositional trendof the silicate melt inclusions, textural features, and modellingwith pMELTS show that the parental melt evolved by major clinopyroxeneand minor olivine crystallization followed by the appearanceof amphibole simultaneously with significant resorption of theearlier clinopyroxene and olivine. The resulting residual meltwas highly enriched in Al₂O₃, alkalis and most incompatibletrace elements. This type of melt is likely to infiltrate andreact with surrounding mantle peridotite as a metasomatic agent.It might also form high-pressure pegmatite-like bodies in themantle that might be the source of the amphibole and sanidinemegacrysts also found in the alkali basalts of the NGVF. Preferentialremelting of the later-formed (i.e. lower temperature) mineralassemblage (amphibole, sanidine, residual glass) might havesignificantly contaminated the host alkaline mafic lavas, increasingtheir Al₂O₃ and total alkali contents and, therefore, reducingtheir MgO, FeO and CaO content. KEY WORDS: silicate melt inclusions; geochemistry; petrogenesis; Nógrád–Gömör Volcanic Field; Pannonian Basin     

西秦岭中生代花岗岩类岩浆作用及成矿

西秦岭是我国重要的有色金属和贵金属成矿省。本文论述了该地区主要矿床的空间分布特点;分析讨论了主要成矿带和矿集区中的矿化组合及其与花岗岩类的空间、时间和成因关系。提出该地区大规模成矿作用出现在220~100Ma之间,最高峰值为170Ma左右。花岗岩类岩浆作用及成矿相应的地球动力学背景为陆—陆碰撞造山运动的晚期表现为一侧陆壳向另一侧陆壳之下的俯冲叠置过程。中生代花岗岩类在成因上与陆壳的俯冲有联系,大多属高钾钙碱性系列。部分为钾玄武岩系列,它们来自加厚的下地壳。部分花岗岩类具壳幔混合成因。一个地区花岗岩类的Pb-Sm-Nd同位素主要受该地区源岩基底地层的控制,因此同一地区花岗岩类具有相近的Pb-Sm-Nd同位素特征。基底地层对花岗岩类的分布成因类型、有关的成矿作用具有重要的控制作用。依据花岗岩Sr和Yb的含量,本文将该地区花岗岩类大致分为两类:埃达克岩和喜马拉雅型花岗岩。铜钼矿大都同埃达克岩有关,而两类花岗岩均可形成金矿。     

Granitoid magmatism of Early Paleozoic orogens

Global manifestations of Early Paleozoic granite formation in the Central Asian Mobile Belt and some other orogenic areas worldwide are considered. The work is based on the author’s studies of Early Paleozoic granitoids from the Altai–Sayan and West Transbaikalian orogenic areas as well as abundant literature data on other world provinces. Special attention is paid to the scales of granitoid magmatism in the Early Paleozoic, its geodynamic settings, periods, and stages, compositional evolution over time, lateral variability in structures of different types, relationship with LIPs, and, correspondingly, connection with mantle plumes and superplumes..     

Experimental Constraints on the Role of Garnet Pyroxenite in the Genesis of High-Fe Mantle Plume Derived Melts

The anhydrous phase relations of an uncontaminated (primitive),ferropicrite lava from the base of the Early Cretaceous Paraná–Etendekacontinental flood basalt province have been determined between1 atm and 7 GPa. The sample has high contents of MgO (14·9wt %), FeO^* (14·9 wt %) and Ni (660 ppm). Olivine phenocrystshave maximum Fo contents of 85 and are in equilibrium with thebulk rock, assuming a of 0·32. A comparison of our results with previous experimental studiesof high-Mg rocks shows that the high FeO content of the ferropicritecauses an expansion of the liquidus crystallization field ofgarnet and clinopyroxene relative to olivine; orthopyroxenewas not observed in any of our experiments. The high FeO contentalso decreases solidus temperatures. Phase relations indicatethat the ferropicrite melt last equilibrated either at 2·2GPa with an olivine–clinopyroxene residue, or at 5 GPawith a garnet–clinopyroxene residue. The low bulk-rockAl₂O₃ content (9 wt %) and high [Gd/Yb]_n ratio (3·1)are consistent with the presence of residual garnet in the ferropicritemelt source and favour high-pressure melting of a garnet pyroxenitesource. The garnet pyroxenite may represent subducted oceaniclithosphere entrained by the upwelling Tristan starting mantleplume head. During adiabatic decompression, intersection ofthe garnet pyroxenite solidus at 5 GPa would occur at a mantlepotential temperature of 1550°C and yield a ferropicriteprimary magma. Subsequent melting of the surrounding peridotiteat 4·5 GPa may be restricted by the thickness of theoverlying sub-continental lithosphere, such that dilution ofthe garnet pyroxenite melt component would be significantlyless than in intra-oceanic plate settings (where the lithosphereis thinner). This model may explain the limited occurrence offerropicrites at the base of continental flood basalt sequencesand their apparent absence in ocean-island basalt successions. KEY WORDS: continental flood basalt; ferropicrite; mantle heterogeneity; mantle melting; phase relations; pyroxenite     

Melting of Amphibole-bearing Wehrlites: an Experimental Study on the Origin of Ultra-calcic Nepheline-normative Melts

Olivine + clinopyroxene ± amphibole cumulates have beenwidely documented in island arc settings and may constitutea significant portion of the lowermost arc crust. Because ofthe low melting temperature of amphibole (1100°C), suchcumulates could melt during intrusion of primary mantle magmas.We have experimentally (piston-cylinder, 0·5–1·0GPa, 1200–1350°C, Pt–graphite capsules) investigatedthe melting behaviour of a model amphibole–olivine–clinopyroxenerock, to assess the possible role of such cumulates in islandarc magma genesis. Initial melts are controlled by pargasiticamphibole breakdown, are strongly nepheline-normative and areAl₂O₃-rich. With increasing melt fraction (T > 1190°Cat 1·0 GPa), the melts become ultra-calcic while remainingstrongly nepheline-normative, and are saturated with olivineand clinopyroxene. The experimental melts have strong compositionalsimilarities to natural nepheline-normative ultra-calcic meltinclusions and lavas exclusively found in arc settings. Theexperimentally derived phase relations show that such naturalmelt compositions originate by melting according to the reactionamphibole + clinopyroxene = melt + olivine in the arc crust.Pargasitic amphibole is the key phase in this process, as itlowers melting temperatures and imposes the nepheline-normativesignature. Ultra-calcic nepheline-normative melt inclusionsare tracers of magma–rock interaction (assimilative recycling)in the arc crust. KEY WORDS: experimental melting; subduction zone; ultra-calcic melts; wehrlite     

试论花岗质深成岩体的复合定位机制及定位空间问题

大陆地壳中巨量花岗岩体的定位机制及定位空间是一个长期急论的问题,已提出十余种机制,但都困难以解决定位空间面引起争议,近年来,人们认识到岩体定位及获取空间是多种机制共存的复合定位机制,这是今后需进一步研究的新课题,笔者提出的复合定位机制可概括为主动膨胀,构造扩展,岩浆侵吞作用３个基本端元机制的构成的复合,可用三角图解表述,并以具体研究实例进行了论述。     

Granitoid magmatism of the Japan and Okhotsk seas

This paper presents a study of Middle Paleozoic, Late Paleozoic, Early Cretaceous, and Early—Late Cretaceous granitoid complexes from two Pacific marginal seas. The granitoid complexes are subdivided into two large groups: (1) mantle-crust derivatives, including andesite differentiates, and (2) crustal palingenetic granites. In terms of formation depth, they are subdivided into abyssal, mesoabyssal, and hypabyssal granites, with decreasing depth from the old to young complexes. It was established that the granitoids of different genesis have peculiar geochemical features. The granitoids of distinguished genetic types differ in the content and proportions of alkalis, primarily, K, as well as Rb, Sr, and Ba. The palingenetic granites show the predominance of K over Na and are classified as high-K calc-alkaline rocks, whereas andesitic derivatives correspond to the calc-alkaline rocks. The former are characterized by the higher Rb and Ba contents, which is related to the geochemical affinity of these elements to K. In contrast, the Okhotsk Sea rocks are characterized by the predominance of Na over K, the elevated Sr content, and the lower Ba and Rb contents. In terms of geodynamic setting, the studied granitoids fall in the field of volcanic arcs and syncollisional rocks. The latters are represented by the palingenetic granitoids of the Sea of Japan.     

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

Abstract: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log m_Au–m_NaCl–T frame fixed linear dependence between log m_Au and T at any studied iso‐pleth (m_NaCl) in the form of log m_Au = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl‐free system in the presence of HMP. In the case, Au solubility increases from (log m_Au) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied f_O2/f_S2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower f_O2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H₂O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H₂O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 m_HCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log m_Pt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous‐chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn‐hydroxides (β–MnOOH, Mn (OH)₂ and Mn₂(OH)₃Cl). These phases are metastable and transfer to Mn₃O₄ with increasing duration. Generation of the Mn‐hydroxides leads to a change of physical‐chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn₃O₄, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn₂O₃–MnO₂ buffer. So at 400C, dissolved Au (log m_Au) increases from –4. 40 in water to –1. 00 in 0. 1 m_HCl, and ones of Pt (log m_Pt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals.