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MINERAL DEPOSITS IN KARST

2002-07-10KDL 1856

MINERAL DEPOSITS IN KARST

29

Rare Metals in the Karst Bauxites from the Apuseni Mountains, Romania

Murariu Titus and Alexandrina Murariu
(Uniersity “Al.L.Cuza”, B-dul Carol I, 20A, 6600, Iasi, Romania)
tmurariu@geo.uaic.ro

The karst bauxites from the Apuseni Mountain-Romania(Padurea Craiului Massif and Bihor Massif) are located in the Bihor Unity (Albioara limestone) an in the Valeni Unity(Farcu limestone and Cornet limestone).

The main components of the bauxites are Al, Fe,Ti oxides as well as the silica. The aluminium is fixed (comprised) in diaspore and in the clay minerals (kaolinite) and in the chlorite. The iron occurs both in its oxidated forms (hematite, goethite) and in its bivalent form (chlorite). The titanium is present in anatase and in rutile. The silica result exclusively from the argillaceous minerals. The other oxides (MgO, MnO, K2O, Na2O, P2O5) vary between trans and hundredths of percentage (Papiu et al,1985).According to the value of the Fe2O3?: FeO ratio, the bauxites are grouped as follows: ferric bauxites, ferroferric bauxites and ferrous bauxites. In the ternary diagram of the three main mineralogical components-(field?II), argillaceous bauxites (field?V) and bauxites(field?I).

The rare metals (Li, Be, Sc, Ga, Zr, Nb) in the karst bauxites from Apuseni Mountains are plotted in the diagram of the ionic potentials in the field of the “bauxitophile” elements. The rare metals content of bauxites is governed primarily by the content of the parent material. The presence of rare metals in the karst bauxites is the result of the following isomorphous substitutions:

2Al3+=2Li++Si4+(kaolinite, diaspore);???2Fe3+=Li++Nb5+(hematite)

Al3+=Li++Be2+(diaspore,kaolinite);?????2Ti4+=Sc3++Nb5 +?(anatase);

Al3+=Ca3+(diaspore,kaolinite);?????????3Ti4+=2Nb5++Fe2+?(anatase);?

Mg2++Fe3+=Li++Si4+(chlorite)?????????Ti4+=Zr4+( anatase);????

Adsorption processes by hydrous Al and Fe3+?oxides have a particular role in the accumulation of rare metals in bauxites.

The rare alkali metal lithium and gallium shows a tendency of enriching in the ferrous bauxites. The presence of lithium, beryllium and gallium in the bauxites is in direct correlation with the clay content (binary diagrams Li : Al, Be :Al, Ga : Al). On the Be: Cr diagram the bauxites are plotted in the field occupied by karst bauxites. Niobium and zirconium rare metals are mostly accumulated in the Ti-bearing minerals (anatase, rutile) of bauxites; zirconium is commonly concentrated by adsorption processes. The features of bauxites were also revealed by the aid of some geochemical parameters:

(Li/Al)×103, (Ga/Al)?×103, (Zr/Ti)?×103, (Murariu and Murariu, 1997) and by some ternary diagrams: Li:Be:Al, Ga:Be:Al, Ti:Zr:Nb etc.

References

Murariu, T., Murariu A.,(1997), Geochemistry of rare metals; Univ. “Al.I.Cuza”. Iasi, 226p;

Papiu, C. V., Mantea, Gh, Iosof, V., Manzatu, S., Udrescu, C., (1985), New chemico- mineralogiccal data on the bauxites in the Galbena Valley (Bihor Mountains); D.??S. Inst. Geol. Geofiz., LXIX/l, p.283-299.

30

Geological Setting, Nature of Ore Fluids and Sulphur Isotope Geochemistry of the Fu Ning Carlin-type Gold Deposits, Yunnan Province, China

P.W Cromie*?& Khin Zaw?+
( Centre for Ore Deposit Research, University of Tasmania
G.P.O.??Box 252-79, Hobart, Tasmania,??7001,??Australia)
*?pcromie@postoffice.utas.edu.au,?+?Khin.Zaw@utas.edu.au

Introduction

Several gold deposits within southern China contain micron sized (<1mm) disseminated gold and are described as having several similarities with the sediment-hosted Carlin-style deposits in Nevada, USA (Cunningham et al. 1988; Ashley et. al., 1991; Lui et al., 1991; Li & Peters, 1998). Carlin-style gold deposits are mostly epigenetic hydrothermal replacement type deposits with associated As, Hg, Sb?+?Tl mineralisation (Arehart, 1996; Ashley et al. 1991).

The southern China Carlin-style gold deposits, are hosted predominantly by Palaeozoic to Mesozoic aged siliciclastic and carbonate lithologies (Fig. 1). They occur along the western margins of the Precambrian South China Block; within the Youjiang margin sag-basin (or the South China Golden Triangle - SCGT), covering an area of approximately 100,000 km2?at the junction between Guizhou, Guangxi and Yunnan provinces (Li & Peters, 1998). Lannigou, Zimudang and Getang, in Guizhou Province as well as Jinya in Guangxi Province are examples of Carlin-style gold deposits within the SCGT that are hosted predominantly by Permian carbonate and Triassic siliciclastic lithologies (Fig. 1). These deposits have reserves of??>30 metric tons of contained gold metal, with average grades ranging from 2 g/t to 8 g/t Au and??some high grade intercepts of up to 16.8 g/t Au (Li & Peters, 1998; Cunningham et al., 1988).?

Further potential for Carlin-type gold mineralisation within the SCGT was identified in Fu Ning County, southern Yunnan Province by Chinese geological teams during the late 1980's with the discovery of micro-disseminated sediment-hosted gold occurring in Devonian siliciclastic units (Fig. 1). The Kuzhubao and Bashishan deposits are most important Carlin-type gold deposits within Fu Ning County, Yunnan Province (Fig. 1).

?

20150206-fig3-5.jpg

Fig. 1. Location map of Kuzhubao and Bashishan Carlin-type gold deposits,

Fu Ning County,??Yunnan Province, China.

Geological Setting and Mineralogy of the Fu Ning Gold Deposits

The Kuzhubao (KZB) and Bashishan (BSS) deposits in Fu Ning County host epigenetic micro-disseminated gold within 1) Devonian carbonaceous mudstone units and 2) along fault breccia zones at the contact between Triassic gabbro and Devonian mudstone units, respectively. Gold mineralisation generally occurs within zones of high deformation, especially where earlier low-angled thrust faults are crosscut by later strike-slip and normal faults. Major sulphide minerals are euhedral and disseminated pyrite, rhombic and acicular arsenopyrite as well as stibnite and minor iron poor sphalerite. Gangue minerals are quartz, sericite, calcite, ankerite and chlorite.??

At least five stages of mineralisation have been developed within the KZB and BSS deposits. The paragenetic sequence at KZB is as follows; Stage I:??sedimentary pyrite, Stage II: quartz-sericite-euhedral pyrite, Stage III: quartz-sericite-arsenopyrite- disseminated pyrite-ankerite+gold, Stage IV: sphalerite and Stage V: quartz-rhombic arsenopyrite-stibnite. At BSS, the paragenetic sequence is; Stage I: quartz-sericite- euhedral pyrite-arsenopyrite, Stage II: Leucoxene, Stage III: quartz-pyrite-arsenopyrite- disseminated pyrite+gold, Stage IV: quartz-sericite-pyrite, Stage V: Chlorite-calcite. Gold mineralisation is closely associated with finely disseminated arsenic-rich pyrite during Stage III at both KZB and BSS. Hypergene ore grades range from 1 to 7 g/t Au and up to 18 g/t at KZB and are also generally < 3 g/t Au at BSS.

Fluid Inclusion and Sulphur Isotope Results from the Fu Ning Gold Deposits

Primary two-phase liquid rich fluid inclusions within quartz during Stages III and V at KZB yielded homogenisation temperatures (Th) of 183o?to 274oC (mean = 210oC) and 178o?to 234oC (with bimodal distributions at 195oand 230oC) respectively.?Fluid inclusion data from quartz associated with gold mineralisation within the Permo-Triassic hosted SCGT Carlin-type gold deposits are similar, with Th values ranging from 165o?C to 290oC (Ashley et al. 1991; Li & Peters, 1998). In comparison, fluid inclusions associated with gold mineralisation within the Carlin-type gold deposits in Nevada have Th values ranging of from 140oC to 250oC (Lamb & Cline, 1997; Cline et al., 1997).

Stage III quartz associated with gold mineralisation at BSS contained primary two-phase liquid-vapour fluid inclusions with Th values ranging from 210o?to 327oC and bimodal distributions clustered at 260o?and 310oC. The Bashishan Th results are also similar to the fluid inclusion Th data from other SCGT Carlin-type gold deposits as previously described by Li and Peters (1998) and Ashley et al. (1991). However, the Th values?at?BSS are much higher than those observed within Carlin-type gold deposits in Nevada by Lamb and Cline (1997) and Cline et al. (1997). Overall, the fluid inclusion Th data from the Fu Ning gold deposits studied so far are possibly suggesting that hydrothermal fluids within SCGT were hotter than the classical Carlin-type gold deposits in Nevada.

Salinity studies of primary fluid inclusions within quartz during Stages III and V at KZB and Stage III at BSS ranged from 0.8 to 13 wt % NaCl equiv. (with bimodal distributions at 2.0 wt % and 12 wt % NaCl equiv.), 0.5 to 7.3 wt % NaCl equiv. (mean = 2.0 wt % equiv.) and 4.3 wt % to 9.3 wt % equiv. (mean = 6.0 wt % equiv.) respectively.?In comparison, primary fluid inclusions within gold ore stage quartz at the Getchell Carlin-type gold deposit in Nevada yielded salinities of 2.9 to 4.8 wt. % NaCl equiv., and up to 8.5?wt % NaCl equiv.?within secondary inclusions (Cline et. al. 1997). Overall, salinity data from the KZB and BSS gold deposits are broadly similar to those observed at the Getchell Carlin-type deposit.

Gases detected by Laser Raman spectroscopy within primary fluid inclusions from Stage III quartz at KZB were predominantly CO2?rich with minor N2?in a 4.5:1 ratio respectively. Primary fluid inclusions at BSS were either N2?or CO2?rich with trace CH4.

Sulphur isotope studies showed that?d34?values for pyrite and arsenopyrite associated with Stage III mineralisation at KZB and BSS range from +9 to +15 per mil. The?d34?values for pyrite and arsenopyrite within the Carlin-type deposits in Nevada have a slightly broader range from +2 to +20 per mil (Hofstra, 1997).

Conclusions

The origin of hydrothermal fluids that formed the SCGT Carlin-style gold deposits is currently inferred by Ashley et al. (1991) and Lui et al. (1991) as primarily from a low-sulphidation epithermal environment with influence from meteoric waters. Geochemical data from this study suggest that hydrothermal fluids within the Fu Ning Carlin-type gold deposits contain some basinal brine characteristics due to: 1) the presence of moderately saline fluid inclusions within Stage III quartz associated with gold mineralisation and 2) moderately heavy sulphur isotope results within Stage III arsenopyrite and pyrite associated with gold mineralisation..

Acknowledgements

The authors would like to thank BHP Minerals and the Centre for Ore Deposit Research, University of Tasmania for supporting this project.

References

Ashley, R. P., Cunningham, C. G., Bostick,??N. H., Dean, W. E.and Chou, I-M.,??1991. Geology and??geochemistry??of three sedimentary-rock-hosted disseminated gold deposits in Guizhou Province, People’s Republic of China.?Ore Geology Reviews, 6,??p 133 - 151.

Arehart, G. B., 1996.Characteristics and origin of sediment-hosted disseminated gold deposits:??A review.??Ore Geology Reviews, 11, p 383 - 403.

Cline, J.S., Hofstra, A, Landis, G. and Rye, R., 1997. Ore fluids at the Getchell, Carlin-type gold deposit, north-central Nevada.?Society of Economic Geologists - Guidebook Series,?28,?p 155 – 166.

Cunningham, C.G., Ashley, R. P., Chou, I-M., Huang,??Z., Wan,??C. and??Li,??W.K., 1988. Newly discovered sedimentary rock-hosted disseminated gold deposits in the People’s Republic of China.?Economic Geology, 83,??p 1462 - 1467.

Hofstra, A.H., 1997. Isotopic composition of sulphur in Carlin-type gold deposits: Implications for Genetic Models.?Society of Economic Geologists - Guidebook Series,?28,?p 119 – 129.

Lamb, J.B. and Cline, J.S., 1997. Depths of formation of the Meikle and Betze/Post deposits.?Society of Economic Geologists - Guidebook Series,?28,?p 101 – 107.

Li, Z. and Peters, S.G., 1998. Comparative geology and geochemistry of sedimentary rock-hosted (Carlin-type) gold deposits in the People's Republic of China and Nevada, USA. USGS open file report 98.

Lui, D. S., Tan, Y. J., Wang, J. and Lui L. L., 1991. Carlin-type gold deposits in China.?In. Brazil Gold ’91, p 89?–?93.

31

Influence of Karst on the Location and Quality of?Limestone Deposits of Lithuania

Vyda Elena Gasiūniene?
(Deputy director, Geological survey of Lithuania)

Abstract

Limestone bed of Upper Permian Naujoji Akmene Formation (analogue of Zechsteinkalk cycle (Cal) of Lower Zechstein Z l in Western Europe) occurred close to surface only in Northern Lithuania is the most important source of carbonate raw material. Upper Permian bed of carbonate rocks (up to 38 m thick, usually 10-20 m) occur under 3-15 m thick cover of Quaternary, sometimes Jurassic and (or) Triassic sediments also. Modem subpermian relief is rather uneven as well as slightly inclined south-westward and westward. Full section of carbonate rocks is composed of three groups of strata: lower clayey limestone, intermediate - limestone and upper - dolomite. Most often the bigger part (60-100%) of the bed consists of limestone rocks: microcrystalline slightly clayey chemogenic limestone and slightly clayey dolomitized limestone. Other sorts of limestone are less wide-spread. Mineral composition of carbonate rocks depends particularly on sedimentary conditions of its forming- values of CaO, MgO and insoluble residuum are the most important indices of limestone quality for practical utilization. However, postsedimentary processes influenced the quality and conditions of occurrence of limestone bed significantly. One of main postsedimentary processes was karst denudation. Due to tectonic deformation and karst denudation processes the former continuous Upper Permian limestone layer at present often is in shape of separate block segments or only relicts, restricted by zones of intensive karst denudation forms. The following denudation forms should be distinguished according to scale of development and their influence on location and structure of limestone deposits: paleoerosion ravines (paleovalleys), paleokarst ravines, surficial paleokarst cavities, internal paleokarst cavities and plane denudation areas. The paleovalleys are the largest denudation forms in the region and are of two types according to their morphology and genesis. The paleokarst ravines cross the limestone bed often as narrow splits. The surficial paleokarst cavities are mostly distributed near to paleokarst ravines. Internal paleokarst cavities were detected by drilling works in various parts of the limestone bed except the lower one. According to remnent of limestone layer, four areas with different denudation level are distinguished. All mentioned processes determines the location, structure, quality and exploitaion conditions and finally the economic viability of limestone resources.

The most intensive processes took place during the continental period of Early and Middle Jurassic and that after the Late Jurassic lasted about 140- 145 mln. years, also during Kimmerian and Alpine tectonic epochs as well as of Quaternary period. Investigation of karst denudation processes and forms are important from the practical point of view. Reconstruction of the former geological processes allows to forecast the most promising areas for exploration of limestone deposits. The second reason of investigations is the cases of reactivation of paleokarst - such phenomena have already been noted in Belgium and Ukraina. Intensive pumping of groundwater from to largest Lithuanian limestone quarries in this area is in progress here and cause dewatering of surroundings in the neighbourhood. Sinkholes may not appear as long as the constant groundwater depression is maintained, because the resulting (if this process is going on) dray cavities can be rather stable. However, upon interrupting the quarry operation, the whole layer will be rewatered, and then sinkholes may form in the relatively stable paleokarst region.