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Geology of the Cluggerfluorite Deposit

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Geology of the Cluggerfluorite Deposit Revista Brasileira de Geociências 17(3): 288-294, setembro de 1987 GEOLOGY OF THE CLUGGE RFLUORITE DEPOSIT. MATO PRETO. PARANÁ. BRAZIL ROBERT E. JENK INS n- ABSTRACT The Mato Preto fluorite deposite are located in the Ribeira River valley 80 km NNE from Curitiba, Paraná, Brazil. They consist of three known orebodies and numerous minar occurrences wi­ thin an area of about 15 km ê. Clugger, the largest dcposit, is a hydrothermnl replacemcnt and fracture-fil­ ling type in a brecciated and sheared contact zone among carbonatitc, nephellne syenitc, phonolite, and tin­ guaite of the Cretaceous-Paleocene age Mato Preto Igneous Complex. Fluorite occurs LS four subparallel but coalescing ore lenses which forro envelopes about dikes of phonolite-tinguaite and have strlke lengths of 250 m, aggregate thickness up to 80 m, and extend to at least 120 m in depth . Dikes and Ienses strike N50-55E and dip steeply to the northwest. Fluorite forms matrix replacemcnts and crosscutting veins in premineral and intermineral breccias adjacent to dikes. Fluorite mineralizatioo has been introduced in at least two pulses and is associated with barite-celestlre, apatite, rare earth minerais, and sulfides. Late explosive venting of the system has formed pipes of volcanic breccia with crackle breccia in ore adjacent. Fluorite along breakage planes is recrystallized into monomineralic veinlets. Mineralization is associated with fracture controlled epidote aJteration, but major silicification apparently predates ore. The c1ugger deposit was probably fonne d at low pressures and temperatures, possibly within a vent of a now-eroded Mato Preto volcano. RESUMO Os depósitos de Iluorita de Mato Preto situam-se no vale do Rio Ribeira, 80 km a NNE de Curitiba,Paraná. Consistem em três corpos de minério e numerosas ocorrências menores numa área de cerca de lSkrrr'. Clugger, o maior dos depósitos, é do tipo substituição hidroterma l e preenchimento de fratura, em zaga de contato brechada e cisalhada, entre carbonatito, nefelin a-sienito, fon6lito e tinguafto do Com­ plexo Igneo Cretãclco-Paleocênlco de Mato Preto. A Iluorita ocorre como quatro lentes subparaleles e coa­ lescentes de minério, as quais constituem envelopes ao redor de diques de fonõlito-tinguafto, com extensões superficiais de 250 m, espessuras acumuladas de até 80 m e extensões verticais de pelo menos 120m. Os diques e as lentes têm direção N50-55E e mergulho acentuado para noroeste. Em brechas de eventos "pré e interminerallzação", adjacentes aos diques , a fluorita substitui a matriz e forma veios intercruzados, respectivamente. A mineralização foi introduzida em pelo menos dois pulsos e está associada com bartra-celestita, apatita, minerais de terras-raras e vários sulfetos. Manifestações explosivas tardias do sistema formaram pipes de brecha vulcânica, assim como brechas do tipo crackle brecc ía no minério original. A Iluortta, ao lon ~o dos planos de fratura. encontra-se recristalizada em pequenos veios monominerálicos. A minerallzaç ão está associada a processo de epidotizaçâo controlada por fraturas e posterior à sllicificeção principal. O depósito Clugger foi provavelmente formado a baixas pressões e temperaturas, possivelmente no conduto de um vulcão atualmente erodido em Mato Preto. INTRODUCTlON Although lhe important assoeia tion of REGIONAL GEOLOGY The dominanl lithologic units fluorine mineralization with siJicic-alkalic igneous rocks is of the Ribeira River valley consist of low to medium grade well documented in the geologic líterature, the coincidence of metamorphic rocks of the middle to upper Proterozoic age major fluorit e deposition with silica- undersaturated and Setuva and Açungui groups as welJ as gran ites and " grani­ carbonatitic rock types appears tc .be much less common. This toid" rocks of the Upper Proterozoic age Três Córregos report describes a large new fluorite deposit at Mato Preto, Complex (Fig. I, Tab. I) . Brazil, in which mineralizatio n ís spatially associated with and The rocks of the region are broken into a number of probably geneticalIy related to carbonatlte. nepheline syenite, structural blocks separated by large northeasterly trending phonolite, and brecciated equivalents. faull zones (Fiori et aI. 1984, in Ronchí 1986). Faultsare The Mato Preto fluorite deposits are located in the upper marked cither by a single zone o f movement and breakage or valley of the Ribeira Rivcr, northern Paraná Sta re, Brazil, by a concentra tion of minor fractures. Severa! periods of Curitiba, capital city of Paraná, is 80 km south -southwes t, reactivation are indicated. Each structural block is and Cerro A zul, a small agricultural community , Iies 22 km to charac terized by relatively distinct stratigraphy and structural the west (Fig. 1). The deposits are located in thickly vegetated orientation. The latter is thougbt to relate to rotation and/or mountainous terrain at clevations of 400 ~ 535 rn. inclination of individual blocks relative to others. Mineralization occurs at a number of locations in an area of The Mato Preto locale lies essentially at lhe junction of about 15 kmê. two blocks, along the trace of the Morro Agudo fault zone. Three fluorite deposits bave been investigated, but this "Granitoid" rocks of the Três Córregos Co mplex crop out report describes onIy lhe geology of lhe Clugger ore body, lhe abundantly in the block to lhe west, while phyllites, most important in that it contains about 80% of known quartzites, and marbJes, tentatively assigned to the Água reserves. A later paper will describe its geoc hemistry . Clara Formation of the Setuva Gro up (Tab. 1), occur to the Informa tion herein presented is lhe result of exploratio n east. The fault has pro bably played an important role in the conducted by Du Pont do Brasil S .A . duri ng the period localization of Mato Preto mineralization. 1982-1985. Coincident with extrusive magmatism in the Paraná Basin The Clugger orebody is the largest fluorite deposit to the west and north, igneous activity was renewed in the presently know n in Brazil with reserves of 2.65 million tonnes Ribeira River rcgion duri ng the Jurassic (Ulbrich & Gomes in proven and indicated categories. Average grade of the 1981). Nurncrous dikes of diabase or diorite were initially orebody is 60.0 wt%. intruded along NW trending fractures, and these were * Ou Pont do Brasil S.A . Alameda Itapicuru, 506, Caixa Postal 26, CEP 06400, Barueri, SP, Brasil Rtvista BrasUeira de Geocilncias.Volume 17,1987 289 Volta Grande, Brás, and several minor occurrences at Mato Preto. Deposits at Mato Preto and Barra do Itapirapuã are míneralogícally complex in that fluorite is associated with apatite, rareearth minerals,and sulfides. LOCAL GEOLOGV Igneous complex AlkaIine rocks and carbonatite of the Mato Preto I~eous Complex crop out sparsely over an area of about 4 km to the north, northwest, and southwest of Mato Preto village. The complex is easily distinguished on 1:25,000 and 1:60,000 scale aerial photography as four adjacent circular structures with attendant- radiating and concentric features. Each circular structure has a diameter of about I km (Fig, 2). Rock types of the complex include large amounts of calcite and ankerite carbonatite, nepheline syenite, phonolite, and ts tinguaite with lesser quantities of ijolite, melteigite, and A\kaline intr-usive eock s volcanic breccía. Abundant fragmentai debris of one aIkalic r-as Córregos Complex (~gronjlo;dMrock$) type in another illustrates a complicated age sequence. Alkalic A~ungu; Group (rnetarnorph;c rccks ) Setuvo Group (melarnorpll;, rOckS) rock nomenclature used here follows that of Streckeisen Faults anel lineornenls (1967). stuorite deposits Ankerite and calcite carbonatites are the most abundant rock types of the igneous sequence and form a central plug in each of the circular structures. Ankerite carbonatite appears to be somewhat more abundant in the area designated Mato Figure 1 - Location and regional geology ofthe upper Ribeira Preto 1 (Loureiro & Tavares 1983), while the calcitic variety River valley, northern Paraná. southern São Paulo. Brasil more widespreadin the complexo (Algarte et ai. 1972, modified} Nepheline syenite occurs inapparently ísolated bodíes near the margins of circular structures at the northend of Clugger and to lhe southeast of FS-P structure (Fig, I). 1t is also followed by injection of phonolite dikes along NE and E- W found as float in trenches at Mato Preto 1 together with structures and by the emplacement of several plugs, chinmeys, phonolite porphyry. Age relationships between them are not and compound aIkaline stocks with compositions ranging known. from limburgite to carbonatite. Petrologic studies of Phonolite is abundant at Mato Preto and displays a individual stocks at Itapirapuã and Banhadão are described by complex history. ~Phonolite porphyry shows a transitional Gomes (1970) and Ruberti (1984), respectively. Carbonatite contact with ijolite near the margin of the circular structure at Barra do Itapirapuã and Mato Preto is reported by Lou­ south of FS-P (Fig. I). 1t also occurs as scattered float at reiro & Tavares (1983)-. Mato Preto I and as abundant fragments in carbonatite. A phonolitic tuff-agglomerate overlies carbonatite in an apparently flat-liyng sheet over a broad area 0.5 km south of Table 1 - Regional stratigraphy of the Ribeira Ríver valley FS-P. Phonolite and tinguaite dikes occurring at Clugger are (Compiledfrom Silva et ai. 1981, Chiodi F~ 1984, Hasui et ai. describedelsewhere. 1984) Rocks of the ijolite-melteigite series occur
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