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, , 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. 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 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, , 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 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 in small quantities near the margins of all four circular structures and also as float throughout the Pinheirinho region to the east. Perlod Group or Formallon LUhologies Ijolite appears to be much more abundant than melteígite, Dikes, chimneys,andstocksof while urtite has not been recognized. Volcanic breccia is ." Juressic- Alkalineintrusíve Banhadão, Itapirapuâ, MatoPrelo, found as three small pipes at Clugger, several at Mato Preto 1 Cretaceous rocks Tunae, BairrodaCruz,José ~i and one at Pinheirinho. Fernandes andothers Porphyritic to equigranular granite, The southward extension of the Morro Agudo fault zone "Granitoid" microgranite and alaskite,more passes through rocks of the complex just to the south of rocksI'Frês thanhalfcompcsed ofhybrid Córregos) mixturesof igneousmaterial with Clugger where it trends about N60E. This zone of shearing ~ Setuvarocks,BrazilianCycle inage and brecciation varies from 50 to 500 m in width and is manifested geomorphologically by linear stream valleys and S" ~ meta-conplomerates, marbles, J Pormation andcalc-silicete rocks, otherwise truncated topography. The circular structures e 8.E generally immature .. ~

A A' 5 " .. , ' .. , " ...... , . '" "''' .. , ", "r \':,·\~ ... . " ... ~ "1'1 .... , '; .: 2 460 ...... "' ·• ...... ' ...... ,..."., "' .. z• r"". • • ...... ;;-:. ' .' 420 ':

3 • a' 500 '':.:· ?\ . ,~ • -r-

460 o ' m 2 · Fluor it e minero liz c;Jlio n Jj:l r'le - me tt eiqit e ·• Anker ile ( o r bono l i l e ~ A ik,o l ine r o ck .., u lH l i lf. ~• 4 20 Co leite cor bo no t ; l . O Pr e ca m bri on rocks. un dift , Phonotit ic I uff -09glom @' f o t e ri'JEl Sheor o nd ' o u l t zon c-s Nep he line ~y e n i t e r:" PhotO· ir. t e r p r e l t' d str ue tu res 38 C C' Figure 2 - Geology ofthe Mato Prelo Igneous Complex

Clugger tluorite consists of fracture fillings and selective 500 replacements of reactive host rocks, mostly caIcite carbon atite. Host rocks have beco extensively brecciated by seve ral processes (as described below); and tluorite has ·• 4 6 largely replaccd breccia matrix. Distribut ion of ore is thus ·~ controlled both by placement of igneous dikes and by ~ distribution and nature of breccias. 4 20 ,OOOOE I0 2 0 0 E

1------t-- - - - + - - --- t------t--- 'l)200tl • Figure 4 - Cross-sections of lhe Clugger orebody ilegend same as Fig, 3,' diagonal rule = epídote alteratíon; horizontal equa/s vertical scale}

lateritic soils at vertical depths to 70 m. Latertzation, largely of carbonatite and phonolite, has poduced hard compact soils, consisting of montmoriJIonitic clays, kaolinite, iron, and aIuminum oxides; quartz and residual flakes o f micas; and apatite. Dense concretionary masses of specular hernatite, • maghemite (?) and manganese oxides up to 10 x 10 x 20 em also occur within 5 to 10 m of lhe sur face. In ore, nepheline 1 syenite, and volcanic breceia weathering produ ets penetrate ~ o .... ';0 fractu re surfaces and vugs but are easily removed by washing. L1THOLOGIC DESCRIPTIONS The deseriptions below apply only to rock units and ores present at Clugger. Figure 3 - Geoíogy of lhe Clugger orebody, MaIo Prelo ( + = They are the result of outcrop mapping at 1:500 and 1:5,000 carbonatíte or weathered equivalem. weatnered scales, study, and sampling of 1.6 km of surface trenches and phonolite-tinguaite; Iriangle = volcanic breccia; stipple = 130 m of undergro und workings and logging of more than fl uorite mineralization (+ 34 wt%); stipple + bar = "fresh" 6,500 m (76 holes) of NX wireline core. Fifty-e ight thin phonolite-tinguaite; rectangle = nephe/ine syenite) sections were examined and studies werc eondueted using the electron probe microana1yzer and X-ray diffraction .

Thc Mato Preto region is strongly but erratically Rock Units CARBONATrrE Calcite car bonatite is a weathered. The orebody itself shows development of red " dense white to light brown roek composcd of a tightly Revista Brasileira de Geociências. Volum e 17. 1987 291 interlocking mosaic of subhedral to euhedral calcite. Grain considered economic at the present time. size varies up to 10 mm but averages around 2 mm. Paulo Adib Engenharia (1986a) calls attention lo the Carbonatite ar Clugger is seldom free from fragmentai deb ris banded natu re of much surface ore. These breccias appear to and is consequently c1assified as breccia. The term, be a product of inter-mineral movement on lhe Morro Agudo carbonatite, is thus utilized to describe both breccias and faull zone. Banding is manifested by subparallel alignment of c1ast-free varieties. Fragmented materiais include phonoJite, breccia fragments, vugs, iron oxide-stained fractures, and nepheline syenite, granité, and phyllite. Fragments are post-fluorite quartz-chalcedon y veinlets. Oriented layers have sometimes rounded but more commonly angular to a few centimeters in thickness, and their trend is N50 ~ 70E subangular. They range in size up to 10 m but are usually on with steep northwesterly or vertical dip. Breccias are largely the order of 5 to 10 em in maximum dimensiono Trace matrix-suppo rted, fragments comprising 10-70 vol% of the minerais in carbonatite include aIkaIi feldspar, biotite, apatite, ore but averaging about 30%. Fragment size averages zircon, pero vskite, and monazite. None has been observed in approximately 5 em. The matrix is more or Iess completely quantity greater than 1 vol%. replaced by fine to coarse-granular fluorite, NEPHEU NESYENrrE II is a rock unit much less . Banded mater ial grades over distances of 1 m or less into abundant than carbonatite at Clugger. 11 is exposed in massive breccia ores. These are very similar in character but trenches only to the north and west of mine coordinates, lack preferred orientation. Fragment size may also range up to l0080N, IOIOOE (Fig. 3) and is also cul in driU hoIes of that severa! meters, and vugs are somewhat more abundant. In area. The syenite is a pale yellow to brownish yellow rock some locations, notably the underground workings (mine composed of 60- 80 vol% alkali feldspar laths in a matrix of coordinates: IOO30N, I OO80E, (Fig, 3), fluorite fragments nepheline, apatite, and aeglrine-augite. AIkali feldspar prisms occur in the fluorite-replaced matrix. average 8 mm in length. Nepheline occurs as anhedral grains Adjacent to the large volcanic breccia pipe previously and aggregates comprising the bulk of matr ix. Apatite as described, fluorite ore has been fract ured into a coarse crackJe euhedral prisms to 2 mm makes up 5- 8 vol% o f the rock. breccia. Randomly oriented and crumpled fracture planes are Aegirin e-a ugite is a trace constituent, At the 450 m elevation spaced 10 cm to 1 m apart, and Iragrnentation extends up lo and beJow nepheline syenite appears to occur as a single mass 80 m from lhe central pipe. The crackle breccia localizes but extends upward as two or three dikelik.e apop hyses (Fig. recrystalJization in the ores and is particularly abundant ncnh 4a). and east o f mine coordinates. 1OOSON , 10100E (Fig. 3). lhe PHONOLlTE AND T1NGUArrE Phonolite and tinguaite recrystallized ores consist of veios and veinlets of coarse to occur throughout the orebody arca as NE trending dikes (Fig. very coarse-grained fluorite which foJlow breakage planes in 3). Phonulite is a dense aphanitic to porphyritic-aphanitic rock the crack le breccia. The veins range up to 1.5 m in thickness of dark green to green-black color, It IS composed of 40 ­ and frequently open into crystal-Iined vugs, 5 to 15 em in 70vol% anhedral lo euhedral nephelioe and 30-40vol% diameter. Fragments from the earlier breccias are rare to cuhedral to subhedral aegirinc-augite, with up to 25 vol% absent. alkali feldspar (grading into ijolite and feldspathic ijolite), Phenocrysts of nepheline and ver y occasional alkali feldspar MINERALOGY Clugger ore is mineralogicaIly complex range to 1 cm in maximum dimension.but are not abundant. (Tab. 2) with about 60 species now known fro m the ores, Trace constituents include biotite, magnetite, apatite, and breccias, and altered wall rocks (Jenkins et ai. 1984, Paulo pyrite. Tinguaite is mineralogically similar, with more Adib Engenharia 1986b, Nuclebrás, oral comm. (986). This is nepheline and less pyroxene. Its color is medium to dark green with strictly aphanitic texture. Phonolite and tinguaite may grade into one anot her along the tren d of a single dike and are Table 2 - Mineralogy o/ lhe C/ugger orebody not mapped separately. In that phonolite also occurs as fragments in carbonatite more than one generation is indicated. Aegirine-augite I R lImen ite I VR VOLCAN/C BRECC/A Well-exposed in lhe northerrnost Albite I C Ilrnenorutile 3 VR An atase 3 VR Kaolinite 3 VC trench at Clugger near mine coordinates 10125N, IOO75E Anglcsite 3 VR Maghemite (7) 3 R (Fig. 3), volcanic breccia there represents a pipe with a Ank erite I C Magnetite 3C diameter o f about 60 m. SmaJler pipes occur to the south and Aragonite 3C Malachile 3 VR west. Volcanic breccia is a somewhat poro us, light brown Arfvedsonile IR Molybd enile 2VR Baríte 2C Monazite 2R rock composed o f pyrite cubes, broken feldspar laths and Bastnaesite 2R Mon tmorillon ite 3VC fragmentai debris in a matrix of glass shards. Fragment Biot ite 3 VC Nepbelíne 2 R materiaIs include violet fluorite, granite. quartzite, and Calcite I VC Opal 3VR phyllite and range to 15 em in maximum dimensiono Celestite 2 VR Perovskite IR Ceruss ite 3 VR Ph logopite I C Fragments are mostly subro unded to rounded, possibly in Chalcopyrite 2 VR Pyrite 2 VC response to assimilation. The volcanic breccia pipes are Chlorite 2 R Pyrolusite (1) 3 R thought to be the result of near-surface explosive activi ty. In "Crandall ite' 3 R Py rrho titc 2 R that they appear to cut ali other rock types and contain Diop side 2 R Quartz 2 R Dolomite IR Rhabdophane (?) 2 VR fragments of Iluorite, they are cer tainly late in the Epido te 2 VC Rutile 3 VR intrusion-mineralization sequcnce. Ferrimolybdite 3 VR Sa nidlne I C ORE BRECC/AS Mosl of lhe ores at CIugger are Fluorapat ite I C Sc heelite 2 VR brecciated to greater or lesser degree. Ores fali into four Fluorite 2VC Siderite IR Ga lena 2VR Sp haJerite 2R general types, disseminated, banded, massive. and Gea rksutlte 3 VR Stro ntianite 3VR recrystallized, each with its distinct style of brecciation. Goethite 3C Talc 3 VR Banded and massive ores constitute aboul 85% of lhe orebody Grossular 2 R Ti tani te 2R and recrystallized most o f the remainder. Disseminated ores Gypsum 3R T remo lite 2R Hematite 3C Vanadinite (7) 3 VR are volumetricaJly unimportant. Hydrogrossular 2 VR w oll astonite 2 R Disseminated material occurs in carbonatite host below the Hydromica 2C Z ircon I R zone of laterization. It consists of single cubes and fine to medium -granular Iluorite which most often replace calcite on I = wall rock; 2 = ore + hydrothermal alteration; 3 = soil + late alteration. VC = very commo n; C = co mmo n: R = rare: VR = very thc rims of fragments in breccia. Disseminated material is not rare . 292 RevistaBradlelrade'Geooíêncías, Volume 17,1987 a function not only of the mineralization process but of the and violet fluorite in brecciated phonolite porphyry and ijolite variety of host roeks. Replaeement of eaeh of the latter has within 10 m of the surface at anelevation of 425 m about 0.7 produeed overlapping but míneralogically and geochernically km southwest from Clugger. This location is within the distinet suites. Weathering of eaeh has added to the Morro Agudo fault zone. eomplexity. At least, three generations of fluorite are present at Clugger. From oldest to youngest these are violet ce FI Py Ep Di+Gr Vólume per ce nr (disseminated and some massive), colorless to brown (massive o ~ O 50 O 50 O 50 O ~ and banded), and colorless-recrystallized. Violet material occurs in the nepheline syenite area and in earbonatite below the zone of surface weathering. In the former case, it is medium to coarse-grained and is associated with barite, apatite, iron oxides, very minor pyrite, a "] crandallite, and other mineraIs. In carbonatite, it is fine to So . medium grained and associated largely with pyrite and , • :'\ epidote. In breceias eontaining fragmented fluorite lhe clasts ~• are violet, the matrix colorless to brown, In drilI holes DB-44 a• and DB-46 (mine coordinates: lOO54N, 9931E, Fig. 3), carbonatite containing abundant violet fluorite is cut by large S5 veios of brown material. < •• Colorless to brown massive or banded fluorite is abundant in the central and southern portions of lhe orebody. It is ) associated with apatite, monazite, bastnaesite, small quantities '00 of pyrite, quartz, and other mínerals. Vugs are partially fílled l.Z:l Epidote cltérution with kaolinite, gearksutite, strontianite, aragonite etc. Similar E2J Tingua ite vug fillings are present in openings in the recrystallized veins. Q ccr-ccnctüe Quantity of fluorite present varies with ore type (Tab. 3).

ALTERATION Hydrothermal alteration accompanying Figure 5 - Mineralogic changes across epidote alteration zone, mineralization at Clugger has been obscured by surface drill hole DB45, lOO37N, 9954 E, Elev. = 524 m (Cc = processes. Any attempt at deciphering the alteration type and calcite; FI = fluorite; Py = pyr/te; Ep = epidote; Di + Gr = sequence must thus be largely confined to the carbonatites diopside + grossular) and ores eut by drill cores below 70 m. The most prominent alteration types include replacement of ealcite by siliea ± fluorite ±pyrite and replacement of PARAGENESIS AND AGE OF silicate minerais by epidote ± albite ± chloríte ± caleite. MINERALlZATION Clugger mineralization is Kaollnization of feldspars in carbonatite may at Ieast in part temporally divisible into three main stages (Fig. 6). They are be related to hydrothermal processes. easily distinguished based on color of fluorite, style of Silicification accompanied by weak fluoritization and mineralization as well as trace míneralogy, OnIy lhe major pyritization, well displayed at Mato Preto I and elsewhere at phases are shown on the diagramo Mato Preto 2, probably represents a deutéric process within Early violet fluorite was in part contemporaneous and in the igneous complex, perhaps unrelated to the activity whieh part later lhan epidotization and pyritization of the host rocks formed the Clugger orebody. Silieified earbonatite has only (A-B of diagrarn). Significant Ba-Sr míneralízatíon was been observed in outcrop at elevations above 510 m. It may formed with lhe fluorite, particularly in lhe nepheline syenite. thus form ao outer alteration shell within the carbonatite Apatite from the host rocks was incorporated in the ores. instrusion(s) of the eomplex. Late silieifieation has been Middle stage, colorless to brown, banded and massive ores deseribed from many earbonatite complexes (Heinrieh 1966) were introduced during and after shearing and brecciation both as large irregular masses (Temple & Grogan 1965) and (B-C of diagram). Somewhat more pyrite and barite appear to as planar zones eontrolled by fractures (Olson et ai. 1954). have formed at this time, and fluorite deposition was No temporal relationship has been firmly established succeeded by small quantities of quartz in, cross-cutting between silieification and epidote alteration. Silieified veinlets and eoatings. Some of these may be related to earbonatite is cut by dike rocks in Clugger trenches, but lhe weathering. latter have been altered to montmorillonite and other minerals Following explosive venting of the system fluorite in during weathering, obscuring any effect of epidotization. crackle breceia adjacent to vent(s) was recrystallized into a Silicified carbonatites are also cut by massive and banded ores network of monomineralic veinIets (to right of C on diagrarn). which themselves contain sparse grains of epidote veined and It is unc1ear whether further fluorite was introduced at this embayed by fluorite. Silicification and epidotization may thus time. but preexisting trace minerais appear to have been be contemporaneous, but it appears likely that the latter is somewhat younger. "'--'--... EVENl ___ A:.TER"'TlON I MI~ERALll"'TiON L"'lERll"'TION MINER"'L -~" _~ I Epidotization is a fracture-controlled alteration type, ,., restricted to the vicinity of dikes. 1ts intensity falIs rapidly ~p;d"\e calo;l. f~1 within a few meters of an intrusion. Introduced fluorite and Pyril. H , - pyrite, both of whieh are later, oeeur well beyond the Fluo.il. :',j~: Baril. "" , ~ boundaries of epidote alteration, lhough in dinúnishing Ouar!> ",., ' quantity (Fig. 5). Epidotization affeets precursor mínerals in I(oolinil. @ :-- the order: feldspar, pyroxene, nepheline, caleite. Quartz remains unaffected, and biotite is usually chloritized. Intense Figure 6 - Paragenesis among major minerais of the Clugger epidotization appears to be restricted to elevations below oreâooy (A = emplacement o/plwnolite-tinguaite dlkes; B = about 450 m, allhough this may be an effeet of surfaee intermineral shearing and brecciation; C = formation of laterization. Epidote alteration occurs, however, with chlorite volcanic and crackle breccias) Rn'iJ laBrasikira d~ G~od2nda.f , Volume 17, 1987 293

removed from the mineraIization. responsible for silicification deposit onIy minor fluorite and Subsequent weathering of the orebody arca resulted in sulfides. thorough Ieaching ofcarbonate minerais to depths up to 70 m, With renewal of shearing and brecciation along the Morro conversion of rock-forming silicates to clays, quarta, and iron Agudo fault zone a swarm of NE- trending oxide mineraIs and formation of new titanium and rare phonolite-tinguaite dikes is emplaced near the earth-containing phases. Except for oxidation of carbonatite-syenite contact (Fig. 7b) with subsequent epidote accompanying sulfides and deposition of late carbonate and alteration and mineralization (Figs. 7b, c). Fluids affecting thc oxide phases in vugs, fluorite was largeJy unaffected by later follow the planar conduits of the dike-host rock contacts surface processes. and deposit ore minerais as envelopes about the dikes. The Phonolite dike rocks from Clugger have been dated at dikes themselves are to some extent fluoritized, Fluids 65.2 ± 3.3 Ma and 67.0 ± 3.4 Ma by whole rock K-A r introduce fluorite, epidote, sulfide minerais, barite, and some methods (Cordani & Hasui 1968). In that these rocks have quart zo Apatite and monazite Irem the host rocks remain in becn both epidotized and fluoritized these data provide a the replacement ore . maximum age for mineralization. The volcanic breccias are At or near the dose of activity explosive venting of the undated but likely represent part of the same cycle of igneous system fonns pipes of volcanic breccia, resulting in activity. T he CIugger deposit is thus considered to be late development of coarse crackle breccias in ore adjacent. Fluids Cretaceous to earIy Paleocene in age. related to this activity or dcveloping later utilize crackle breccia as channelways and effect rccrystallization and GEN ESIS The intimate spatial and temporal association enrichment of the ore (Fig. 7d). Present erosional levei of the of the Clugger orebody with magmatic rocks, with rare earth, deposit is shown on figure 7d. phosphate, and titanium-niobium mineralization suggest that Any hypothesis for origin of the deposit is hampered by the deposit is hydrothennal in originoFigures 7a ~d therefore the current lack of fluid inclusion ar isotopic data. Proximity ilIustrate one possible scheme for its evoIution. of porphyritic-aphanitic to glassy igneous rocks suggests a relatively shallow depth of fonnation. Projection of elevations Irom the Primeiro Planalto Paranaense (Almeida 1952) A 8 indicates 400-500 m of post-Pliocene erosion, but further quantification is not possible. Similarly, association of fluorite with rather low intensity epidote alteration would seem to indicate a low temperature of forrnation, but no definitive estlmatlon can be made.

Table 3 - vartanons in CaF2 conteru with ore type (vatues in wt% )

Ra nge Average Low IIIgh Dissemi nated (VioleI) < 0.1 40 28 Massive (Violet) 47 65 52 Massive and banded (Colorless) 55 70 61 Recrysta llized 75 94.5 85 The circular structures outlining elcments of the Mato Preto Igneous Complex, the pipes of volcanic breccia and the Ilal-lying phonolitic luff-agglomerales ali suggest lhe existence of a volcanic edifice at Mato Prelo during the late Cretaceous with fonnation of the Clugger orebody in one of the vents. T his edifice was possibly similar to the Napak, Kenya voleano studied by King (1949), but very limited outcrop and drill data outside of lhe orebodies make substantia tion of a Mato Preto volcano difficult.

CON CLUSIONS With lhe exception of Barra do Itapirapuã, the fluorite dcposits of northcm Paraná align ih a prominenl E- W direction (Fig. 1). AI Maio Preto and westward this lineation coincides with a belt of dikes, plugs, and small stocks, mostly of phonolitic composition. The Figure 7 - Schematic cross-sections showing lhe evolutíon of alignment may be happenstance, in that genesis of different lhe C/ugger orebody (ns = nephe/ine syenite; p = ph ono/ite; deposits appears to range fram low tempcrature sedimentary cb = carbonatíte; pt = phonolite-tínguaite; ep = epidote replacemeot (Sete Barras , Lopes et a/o 1980; Volta Grande, alteratíon and /ow grade mineralization: vb = votcanic Ronchi 1986 to that of Mato Preto, but it may also relate to a breccía. solid b/ack denotes hygh-grade mineralízation} Precambrian(?) source for Maio Preto fluorine. The distribution of aeromag netic and aeraradiometric anomaJies show similar patterns. Ferreira & Algarte (1979) Figure 7a depicts injection of a central core plug of calcite propose the existence of ao alkaline magma chamber of carbonatite into nepheline syenite and phonolite (with small approximately 400 km2 extent, elongated E-W and underlying quantities of ijolite). Intrusive breccias are formed at thc the general vicinity of Cerro Azul. Thc Mato Preto locale margins of thc carbonatite body, and the latter is silicified represents the intersection of the NE-t rending Morro Agudo above elevations corresponding to the present 520 m. Fluids fault zone with this deepcr crustal magma source. 294 Revista Brasileira de Geociências, Volume 17, 1987

The 2.65 million tonnes reserve of lhe Clugger orebody Czel. I .R.P. Tavares, and R.H. Fulton for their thoughtful places ir among lhe " world class" Iluorite depo sits. Nearly ali rcvíews of the manuscrip t. Moacir C. de Almeida and I .R.P. of these exce ptionally large deposits, notably those of Tavares are acknowledged for many stimulating discussions Coahuila and Guanajuato, M éxico (Van Alstine et ai. 1962), of Mato Preto geoIogy. N.F. Lima is acknowledged for her are associated with silicic-alka lic igneous rocks. Although secretarial skills. The author is also deep ly 'grateíul to the other cabc natite-affiliatcd dcposirs are known {Heinrich managements of Du Pont do Brasil S.A. and E.I. Du Pont de 1966), Clugger is unusual both for its sizc and for its Nemours & Co. (USA ) for pcrmission to publish these relatively high grade of mincralization. studies, particularly 1.D.B. Lycarião and W.L. Kremcr .

A cknowledgement s The author wishes to thank L.J.

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O desenvolvimento científico e tecnol6gico deve ser norteado pelos seguintes princíp ios: Proporcionar as condições necessárias para que o de­ senvolvimento econômico e social se faça de forma autônoma, de tal modo que se possa superar a dependência tecnol6gica do país e alcançar a melhoria das condições de vida da população. Propiciar garantias efetivas à autonomia da pesquisa científica... A pesquisa de materiais e de fon­ tes de energia será orientada pela busca de alternativas à exploração de recursos naturais não renováveis, bem como da preservação dos recursos minerais estratégicos . SDPC. 1987, propo sta para a Cons tituinte