Research subject. Serpentinites of the apocarbonate type in the contact aureole of the Salmi Batholith. Aim. Mineralogical and genetic description of the calcite-serpentine rocks of the Hopunvaara ore field. Materials and methods. Thirty samples of ophicalcite were studied using scanning electron microscopy, electron probe analysis, powder X-ray diffraction, FTIR and Raman spectroscopy, as well as differential thermal analysis. Results. The ophicalcite of the Hopunvaara ore field is represented by two types. The first variety was studied on samples from the Izvestkovyi quarry (“Lime Break”). It consists of thin-fibrous aggregates of clinochrysotile and lizardite (or only lizardite) intergrowing with calcite, with subordinate amounts of phlogopite and fluorapatite, as well as with veins of magnetite. Serpentine contains a small amount of impurities – up to 1.0 wt % FeO, up to 0.7 wt % Al2O3 and not more than 0.1 wt % MnO. Calcite is chemically pure. Ophicalcite of the second type, described in the Klara mining, is composed mainly of lizardite, which forms complete pseudomorphs after crystals of forsterite and/or minerals of the humite group enclosed among a carbonate matrix. Serpentine contains 0.4–2.5 wt % FeO, 0.0–1.6 wt % Al2O3, 0.1–0.2 wt % MnO, and 0.9–2.1 wt % F. In the carbonate matrix, along with almost pure calcite, there is dolomite containing 1.4 wt % MnO. Minor minerals are represented by fluorite, phlogopite and sphalerite. Such a rock is sectioned by antigorite-carbonate-fluorite-hematite veins with cassiterite, the formation temperature of which is estimated at 300–350°C. Conclusions. The formation of ophicalcite of the first type occurred through the interaction of dolomite with acidic SiO2-rich 200–300°C hydrothermal solutions. The microfiber structure of apodolomite serpentine aggregates is due to the mechanism of their crystallization in a porous medium that occurs during carbonate leaching. Ophicalcite of the second type was formed as a result of serpentinization of forsterite calciphyres at the regressive stage of skarnification process at T < 370°C.

The results of modern studies of the Baimka Ore Zone (BOZ) in Western Chukotka obtained during prospecting and exploration in 2008–2016 are summarized, and the main features of its structure and development are shown. The porphyry–epithermal ore systems of the BOZ were formed within the NW-trending regional-scale dextral strike-slip fault in the Early Cretaceous time. Meridional extensional structures and diagonal strike-slip faults in the strike-strip fault zone controlled the position and morphology of intrusive bodies of monzonites and paragenetically related with them ore stockworks with porphyry copper and gold–silver epithermal mineralization. Ore stockworks were traced to 700-m depth by drilling, and, accordingly to the geophysical data, mineralization is forecasting deeper. The zoning of soil anomalies and the primary geochemical zoning of the Peschanka deposit and the Nakhodka ore field are described. An erosion levels of deposits are different. For the Peschanka deposit, an upper-middle erosion level has been established. For the deposits of the Nakhodka Ore Field, the erosion grade changes from the upper to the lower level. New prospects have been identified within the BOZ, where economical porphyry copper and gold–silver epithermal mineralization is predicted.

Gold deposits associated with granitoid intrusions have long been known. Recently, a class of deposits was identified among them, called intrusion-related granite systems, IRGS (gold-rare metal formation). The standards of the geological prospecting model for them are the deposits of the Tintin metallogenic belt (Alaska, Canada). In Russia, this type has been studied less; IRGS includes the Shkolnoye and Butarnoye (Magadan region) and Kekura (Chukotka) deposits. Based on field and laboratory studies, generalization of prospecting geological and geochemical data, the characteristics and localization features of gold mineralization associated with granitoids of a large igneous uplift in the South Anyui structural-formational zone (Western Chukotka) were determined. The mineral composition of ores, the sequence of their formation were studied, homogenization temperatures and salt concentrations in gas-liquid inclusions were determined. The geochemical and mineralogical zoning of the ore-magmatic system has been identified, and criteria have been developed for assessing erosion and predicting gold mineralization to depth.

The Kekura gold deposit, amongst other volcanogenic Au-Ag, intrusion-related Au and porphyry Cu-Mo-Au deposits in the Western Chukotka, is considered to be of economic importance. It is associated with the central part of the Early Cretaceous stock-shaped three-phase Kekura granitoid intrusive. Gold-bearing quartz veins and lenses occur within the intrusive and near-contact country rocks. The following alterations were recognized at the deposit: (1) unmineralized quartz-calcite-tourmaline-albite-muscovite, (2) propylitic accompanied with rare thin quartz veinlet and pockets containing Sn-W-Cu-Bi-As mineralization, (3) quartz-tourmaline-albite-muscovite alteration rimming quartz-molybdenite veinlets, (4) beresite (quartz-muscovite-dolomite±arsenopyrite±pyrite type) rimming gold-bearing quartz-dolomite veins with arsenopyrite and pyrite, (5) quartz-muscovite-illite-siderite-dolomite alteration containing quartz veinlets and pockets with Au-Ag-Sb mineralization, and (6) rare kaolinite type with disseminated pyrite related to faults. The major economic gold grade is related to the fourth stage. The Kekura deposit combines features of reduced and oxidized intrusion-related gold deposits with the late epithermal mineralization.

This paper is focused on the tourmaline and associated minerals from veinlets cutting chromitite of the Kamennoozerskoe occurrence, which is a part of the Shabrovskoe district in the Central Urals. Tourmaline belongs to the dravite—oxy-dravite solid solution series, contains Cr (0,52–2,06 а.ф.), Ni (до 0,03 а.ф.), V (до 0,02 а.ф.) The Raman spectroscopy indicates Fe 3+ in tourmaline. Rutile associated with tourmaline contains, wt %: 4.68–11.69 Sb 2 O 5 , 2.00–8.02 Cr 2 O 3 , and 0,88–1,14 WO 3 . Combination of high Sb and Cr contents in rutile is established possibly for the first time. It is suggested that tourmaline and associated minerals from the veinlets cutting chromite were formed in oxidizing environment.

The Nakhodka ore field (NOF) is situated in the Baimka Trend, Chukotka, Russia, and comprises the Vesenny epithermal Au–Ag, and Malysh, Nakhodka, Vesenny III, and Pryamoy porphyry Cu-Au ± Mo deposits. Porphyry and epithermal mineralization of the NOF are hosted by Early Cretaceous diorite and monzonite intrusions, which are dated at 139–141 Ma (U–Pb zircon). The NOF mineralization is structurally controlled. The prevailing stress field during the evolution in the Baimka dextral shear zone (also known as Baimka Trend) has led to the formation of extensional and strike-slip structures that control distinct zones with strong quartz-sericite alteration and sheeted high-grade quartz–sulfide veining; characteristics that are similar to the world-class Peschanka porphyry Cu-Au deposit located about 20 km to the NW of the NOF. Four types of hydrothermal alteration are documented in the NOF: (1) potassic, (2) propylitic, (3) quartz-sericite, and more rarely (4) argillic. Two phases of porphyry-style mineralization are distinguished: (1) early-stage quartz-magnetite veining associated with potassic alteration and (2) sheeted quartz-sulfide (bornite, chalcopyrite, molybdenite, pyrite) veining that is spatially associated with a strong quartz-sericite alteration assemblage. Epithermal Au–Ag mineralization belongs to the intermediate-sulfidation type and consists of gold-bearing polymetallic quartz-dolomite ± rhodochrosite veins and veinlets. The NOF is defined by a distinct geochemical zonation. Geophysical data show that the high-grade stockwork zones at the Vesenny III porphyry Cu-Au deposit are defined by pronounced magnetic anomalies reflecting abundant hydrothermal magnetite veining, while the Vesenny epithermal Au–Ag deposit is defined by a strong negative magnetic anomaly due to strong silicification and magnetite-destructive quartz-sericite to argillic alteration.

Porphyry Cu-Au +/- Mo mineralization at Peschanka is hosted by monzodiorite and monzonite intrusions with high-K calc-alkaline to shoshonitic compositions and dated at about 144.1 +/- 1.5 Ma, using U/Pb zircon ages. The Cretaceous intrusions are emplaced in a melange of Cretaceous island arcs, a tectonic setting comparable with other world-class porphyry Cu-Au deposits, such as Oyu Tolgoi, Mongolia and Pebble, Alaska. Abundant primary magnetite contents of the Peschanka intrusions, as well as numerous gypsum and anhydrite veins, reflect the high oxidation states of their parental magmas. This mineralogical interpretation is confirmed by high whole-rock Fe2O3/FeO ratios and high V/Sc ratios of the rocks of up to 1.27 and up to 21.9, respectively. The whole-rock Eu/Eu* ratios of the Peschanka intrusions are >= 1 which is also typical for potassic igneous rocks with high oxidation states. Abundant amphibole and biotite phenocrysts of the intrusions as well as their high whole-rock Sr/Y ratios of up to 225 document significantly high H2O contents of the highK magmas. Peschanka contains a resource of >9.5 Mt of copper at an average grade of 0.43 wt% and 16.5 Moz of gold at a high average grade of 0.23 g/t and thus represents one of the largest undeveloped greenfield copper projects worldwide. The vicinity of Peschanka still offers significant brownfield exploration potential. The hypogene vein-related and disseminated Cu-Au +/- Mo sulfide mineralization at Peschanka is structurally controlled by significant NE-trending strike-slips that acted as the conduits for the hydrothermal fluids. The central part of the orebody consists of high-grade north-south-trending sheeted quartz-bornite veining with unusually high vein densities. The highest Cu and Au grades are directly correlated with high vein densities. Peschanka is defined by distinct hydrothermal alteration zones including potassic, phyllic, propylitic and argillic assemblages, but a distinct lack of advanced argillic alteration. The mineralization itself is also zoned ranging from a central Mo-Cpy-Bn sulfide assemblage to a peripheral Py-Mt-dominated zone ('pyrite-shell'). Late-stage polymetallic assemblages overprint and surround the main stockwork zone.

Me4+-bearing (Me4+= Sn, Ti) dravite analogs were synthesized in the system MeO2-MgO-Al2O3-B2O3-SiO2-NaO-H2O at 700 degrees C and 4 / 0.2 GPa in four hydrothermal experiments. Tourmalines form rosette-like aggregates and needle-like crystals that are chemically homogeneous. Tourmaline crystals obtained in high-pressure runs (4 GPa) are much smaller (up to 0.1 x 2 mu m) and have lower Me4+ (0.27 wt. % SnO2, 0.57 wt. % TiO2) than those from the low-pressure (0.2 GPa) runs (up to 1 x 5 mu m; 1.77 wt. % SnO2, 2.25 wt. % TiO2). Synthetic analogs of rutile, quartz and coesite were obtained in the system TiO2-MgO-Al2O3-B2O3-SiO2-NaO-H2O, whereas synthetic analogs of cassiterite, tin-rich (up to similar to 19.55 wt. % SnO2) Na-pyroxene, MgSn(BO3)(2) (Mg-analogue of tusionite), quartz and coesite were synthesized in the system SnO2-MgO-Al2O3-B2O3-SiO2-NaO-H2O. We suggest that at a high temperature (>= 700 degrees C), the pressure negatively affects the Ti incorporation into the tourmaline structure. In contrast, at relatively low pressures, the Ti incorporation in tourmaline structures is governed by the Ti content in the mineral-forming medium. Low-pressure conditions are feasible for Sn incorporation in the tourmaline structure. The presence of Ti4+ and Sn4+ cations in structures of the synthesized tourmalines (probably at octahedrally coordinated sites), is also indicated by changes in the unit-cell parameters.

AbstractBlack tourmalines from seven granitic pegmatites (Golodnaya, Kazennitsa, Mokrusha, Kopi Mora, Zheltyye Yamy, Buzheninov Bor and Ministerskaya) related to the Murzinka pluton, Central Urals, Russia have been investigated using electron microprobe analysis, LA-ICP-MS, Raman and Mössbauer spectroscopy. Pegmatites are hosted by serpentinites and gneisses and are classified as schorl, oxy-schorl, fluor-schorl, dravite, oxy-dravite, foitite, oxy-foitite and darrellhenryite. The possible compositional evolution of tourmalines from the Ural pegmatites is as follows: Mg-rich dravite through to Fe-rich schorl, foitite and oxy-foitite to Fe- and Mn-rich darrellhenryite. The major substitutions in the tourmalines are: (1) Fe2+ ↔ Mg; (2) Al + WO2– ↔ Fe2+ + WOH–; (3) X-site vacancy + Al ↔ Na + Fe2+; (4) Al + WO2– ↔ Mg + WOH–; (5) X-site vacancy + Al ↔ Na + Mg; and (6) Fe ↔ Mn. Statical processing of the trace- and major-element composition distinguished three tourmaline groups: (1) trace Co, Ni, Pb, and major Ca and Mg; (2) uni-, di- and trivalent traces (Li, Zn, Ga) and di- and trivalent majors (Al, Mn); (3) U, Th, Hf, Ta, Nb, Y, In, and Sn which correspond to tri-, tetra-, and pentavalent high-field-strength elements. Mössbauer data shows the Fe3+/Fe2+ ratios in tourmalines from pegmatites hosted by gneisses (0.05–0.18) and serpentinites (0.28–0.65), indicates different oxidising environments. Raman data are consistent with the composition of the tourmalines.

Background. Some papers describing the deposits and prospects in the Baimka ore zone (Baimka Trend), the Chukotka Autonomous Region have been recently published. It should be noted that those publications concern with the large Peschanka porphyry copper-molybdenum-gold deposit and Nakhodka ore field. At the same time, some copper prospects were found at the zone flanks and their nature is not clear. There are no data available in the literature that would clarify the mineralogy of hydrothermal alteration and ores at those prospects, including Top and Luchik located at the northern flank. To understand the nature of these prospects, we studied in depth mineralogy of hydrothermal alteration and ores.Aim. This study aims to describe mineralogy of metasomatic rocks and ores from the Top and Luchik prospects in the northern part of the Baimka zone, Western Chukotka.Materials and methods. Several dozen polished thin sections were microscopic studied at the Department of Mineralogy of Moscow State University using an optical microscope. The chemical composition of minerals was determined using electron microprobe at the Laboratory of Analytical Techniques of High Spatial Resolution, Department of Petrology and Volcanology, Moscow State University.Results. It was found that propylitic is the major hydrothermal alteration at the prospects studied here. Metasomatic rocks are cut by mineralized quartz and carbonate-quartz veins. Chalcopyrite and pyrite are the major ore minerals; galena, sphalerite, pyrite enriched in As and Sb, and marcasite are minor; Hg-bearing tetrahedrite-(Zn), native gold with the fineness of ~830, petzite, hessite, and acanthite are rare.Conclusions. The data obtained suggest that mineralization at the Top and Luchik prospect is attributed to the epithermal intermediate sulfidation type. Considering the occurrence of the epithermal mineralization in the upper part of the hydrothermal column and the porphyry mineralization in the Baimka zone, the porphyry mineralization is possible at depth at the Top and Luchik prospects.

The Kekura gold deposit in Western Chukotka, Russia is spatially related to the granitic rocks of the Early Cretaceous Gvardeisky Complex. The deposit was formed during five mineralization stages: (1) cassiterite-scheelite-chalcopyrite-bornite-arsenopyrite, (2) molybdenite, (3) chalcopyrite-gold-bismuth tellurides, (4) arsenopyrite-gold-scheelite, and (5) stibnite-gold-silver. The tetrahedrite group minerals (Ttgs) were identified in stages 2, 4, and 5. In the molybdenite stage Ttgs are associated with digenite, bornite, chalcopyrite, molybdenite, and arsenopyrite. Ttgs from the arsenopyrite-gold-scheelite stage are associated with scheelite, chalcopyrite, sphalerite, galena, and native gold with fineness of 800-850. Along with tetrahedrite, stibnite-gold-silver mineralization includes Ag-Au and Au-Ag-Hg alloys, native silver, sphalerite, stibnite, boulangerite. The molybdenite stage Ttgs display a wide range of the Sb/(Sb + As + Bi) ratio (sb) 0.06-0.85 and a narrow range of the Fe/(Fe + Zn) ratio (fe) 0.78-1.00, and are enriched in Cu (up to 5.767 apfu Cu at the M(1) site); the Ag content does not exceed 0.080 apfu. Ttgs of the arsenopyrite-gold-scheelite stage have the Cu-free at M(1) site, but are highly variable in the sb and fe values, ranging from 0.24 to 1.00, and from 0.14 to 1.00, respectively; the Ag concentration is higher than that in the molybdenite stage Ttgs, reaching 0.365 apfu. The stibnite-gold-silver tetrahedrite has high Ag (up to 3.442 apfu) and sb and fe ranging from 0.68 to 1.00 and from 0.10 to 0.84, respectively. Some Ttgs compositions of the molybdenite and stibnite-gold-silver stages are Bi-bearing that is caused by the replacement of previous Bi-minerals.

Micas from granitic pegmatites of the Mokrusha and Ministerskaya mines within the Murzinka Pluton in the Central Urals are polylithionite, sokolovaite, trilithionite, Li-bearing muscovite, and annite–phlogopite in solid solution. Chromium and magnesium, which are uncommon elements for light mica that were detected in micas from both mines indicate pegmatite contamination by the material of the host rocks. The low K/Rb and Ta/Nb ratios testify to a very high degree of pegmatite differentiation of both mines.

The Kışladağ porphyry Au deposit occurs in a middle Miocene magmatic complex comprising three different intrusions and magmatic-hydrothermal brecciation related to the multiphase effects of the different intrusions. Tourmaline occurrences are common throughout the deposit, mostly as an outer alteration rim around the veins with lesser amounts disseminated in the intrusions, and are associated with every phase of mineralization. Tourmaline mineralization has developed as a tourmaline-rich matrix in brecciated zones and tourmaline-quartz and/or tourmaline-sulfide veinlets within the different intrusive rocks. Tourmaline was identified in the tourmaline-bearing breccia zone (TBZ) and intrusive rocks that had undergone potassic, phyllic, and advanced argillic alteration. The tourmaline is present as two morphological varieties, aggregates of fine crystals (rosettes, fan-shaped) and larger isolated crystals and their aggregates. Four tourmaline generations (tourmaline I to IV) have different compositions and substitutions. Tourmaline I in TBZ and INT#1 is distinguished by the highest Fetot and enriched in Fe3+. Tourmalines II and III occur as fine aggregates, accompanied by the formation of isolated crystals and are characterized by lower Fetot and Fe3+. Tourmaline IV is characterized by the lowest Fetot, enriched in Cl, and has the highest proportion of X-site vacancy among all the tourmalines. Tourmaline I may be attributed to the potassic stage in INT#1 and early tourmaline in TBZ. Tourmalines II and III from INT#1 and the TBZ could be referred to the phyllic stage. The low Fe content in tourmaline is caused by the simultaneous deposition of sulfide minerals. Tourmaline IV from the TBZ and tourmaline II from INT#3 are distinguished by the high X-site vacancy proportion up to the formation of X-site vacant species as well as enriched in Cl; they can be attributed to the argillic stage of the hydrothermal process. The textural and especially chemical data of the tourmaline from the Kışladağ Au deposit provide information on the physico-chemical conditions during the porphyry to epithermal transition and subsequent epithermal overprinting.

The Kekura gold deposit (76.2 t Au at 8.1 g/t) is situated in Western Chukotka, a region that hosts several Au, Ag, Cu, and Mo deposits and prospects. The Kekura deposit is related to the eponymous granite intrusion that is cut by porphyry dikes. The U-Pb zircon age of one of these dikes is 112 ± 1 Ma (2σ) that corresponds to the latest Aptian/earliest Albian. Both intrusion and dikes are hydrothermally altered and are cut by gold-quartz and molybdenite-quartz veins and stringers. Two molybdenite samples yield Re-Os model ages of 112.5 ± 0.6 and 112.3 ± 0.6 Ma (2σ). These Re-Os ages indicate the close temporal relationship between the molybdenite mineralization and the porphyry dikes. The age of the Kekura mineral system is similar to that of the post-collisional granitic plutons of the Anyui zone spatially scattered, between 140 and 210 km northwest of Kekura. We suggest that this temporal relationship may increase the likelihood of further discoveries of economic gold mineralization related to the currently underexplored Aptian post-collisional magmatic complexes of the Western Chukotka area.

Tourmaline from the Solnechnoe hydrothermal granitoid-related tin deposit in the Khabarovsk Krai, Russian Far East has been studied with electron microprobe, infrared and Mossbauer spectroscopy. Tourmaline formed in three distinct stages with different types of chemical substitution. Tourmaline from the first unmineralised stage is classified as dravite or schorl, which could be enriched locally in Ca, the X-site vacancy and F. This tourmaline is characterised by the Fe <-> Mg and X vacancy + Al <-> Na + Fe substitutions. The second, molybdenum-stage tourmaline, is schorl-dravite and fluor-schorl-fluor-dravite enriched in Ca, and a few compositions belong to the calcic group. The predominant substitution is Ca + Mg <-> Na + Al. The third, tin-stage tourmaline, is classified as schorl-dravite with some tourmalines being fluor-schorl, oxy-schorl, foitite and magnesio-foitite. The tin-stage tourmaline is characterised by the substitutions Fe2+ <-> Mg, Al-tot + O2- <-> Fe2+ + OH-, and Fe3+ <-> Al-tot. An increase of the Fe3+/Fe-tot value from 3-9% in the molybdenum stage to 12-16% in the tin-stage tourmalines indicates an increase in oxidation potential, which possibly contributed to cassiterite deposition. Comparison of tourmalines from greisen, porphyry and intrusion-related tin deposits worldwide shows they differ in primary chemical substitutions so can be characterised by this mechanism. The Fe3+/Fe-tot value in tourmaline also appears to be one of the indications for the tin deposit type. The Fe3+/Fe-tot value increases from <10% in greisen tourmaline through 15% in tourmaline from intrusion-related deposits to 20% in tourmaline from porphyry deposits.

Scheelite from the Kekura gold deposit in the Western Chukchi Peninsula is reported for the first time. Three generations of the mineral have been identified. According to the LA–ICP–MS data, the Mo content in scheelite does not exceed 0,2 ppm and total REE ranges from 20 to 150 ppm. The REE distribution patterns of all three scheelite generations have a strong positive Eu anomaly (Eu/Eu*=4,455,6), which is typical of scheelite from intrusion-related and orogenic gold deposits. The high Sr concentration (1300–12000 ppm) is characteristic of the hypabyssal intrusion-related Au deposits. According to the fluid inclusion data, the minimal crystallization temperature of scheelite and associated quartz is 200–250 °С.

Аннотация: Мурзинские самоцветные копи, насчитывающие более 250 пегматитовых тел с редкометальной минерализацией и ювелирными камнями (турмалин, топаз, берилл и др.) входят во всемирно известную Самоцветную полосу Урала.Минералы группы слюд являются важнейшими индикаторами физикохимических условий образования пегматитов и, как правило, содержат значительное количество редких элементов.В работе приведены результаты исследования литий-алюминиевых слюд из копей Мокруша и Министерская.По данным микрозондового анализа, в слюдах из копи Мокруша впервые установлен цезиевый аналог трилитионита в виде прожилков и многочисленных вростков в лепидолите.Результаты ИК-спектроскопии позволяют отличить

Relevance of the work is due to the need to study the mineralogy of gold deposits in the Russian Far East, information about which is extremely scarce. Purpose of the work: study of the chemical composition of tourmaline from Mnogovershinnoe ore deposit, Khabarovsk Krai (Far East). Methodology of research: The chemical composition of minerals and BSE images were obtained using a Jeol JSM-6480 electron microscope equipped with an Inca Energy-350 EDS (analyst is N. N. Koshlyakova, Department of Petrology, Lomonosov Moscow State University). Electron microscope shooting environment: accelerating voltage is 15 kV, measuring current for the sample is 30 ± 0.1 nA. XPP corrections were used for the adjustment procedure (INCA program, version 17a). Results. The obtained data show that tourmalines of the Mnogovershinnoe deposit differ in their chemical composition and type of substitution. All studied tourmalines by these parameters can be divided into two groups. Group 1 includes schorl, foitite, and pegmatoids feruvite, as well as schorl and foitite of the first generation, tourmaline-muscovite-quartz veinlet in sandstones. Group 2 includes schorl of the second generation, tourmaline- muscovite quartz veinlet, schorl and foitite of quartz-tourmaline metasomatites, and cement dravite of quartz breccia. Conclusions. Tourmalines of the post-ore mineral associations of the Mnogovershinnoe gold deposit are divided into two groups characterized by different chemical composition and substitutions. Tourmalines of the first group with substitutions Fe ↔ Mg and X-vacancy + Al ↔ Na + R2+ are confined to pegmatoids and were formed in reducing or weakly oxidative conditions. Later tourmalines of the second group with substitutions Fe3+ ↔ Al and Al + O2– ↔ R2++ OH– indicate a possible porphyry-style mineralization and its formation during lowering oxidative potential.