A five year program of systematic multi-element geochemical exploration of the Catalonian Coastal Ranges has been initiated by the Geological Survey of Autonomic Government of Catalonia (Generalitat de Catalunya) and the Department of Geological and Geophysical Exploration (University of Barcelona). This paper reports the first stage results of this regional survey, covering an area of 530 km2 in the Montseny Mountains, NE of Barcelona (Spain). Stream sediments for metals and stream waters for fluoride were chosen because of the regional characteristics. Four target areas for future tactic survey were recognized after the prospect. The most important is a 40 km* zone in the Canoves-Vilamajor area, with high base metal values accompanied by Cd, Ni, Co, As and Sb anomalies. Keywords: Catalanides. Geochemical exploration. Stream sediments. Base metal anomalies. Principal Component Analysis

Casas i Ponsatí, Albert

Font Cisteró, Xavier

Vaquer Navarro, Ramón

Viladevall Solé, Manuel

Diposit Digital de la Universitat de Barcelona

ACTA GEOLOLOGICA HISPANICA, t. 19 (1984), n." 3, phgs. 193-197 Geochemical exploration in the Montseny Mountains (NE Spain) by X. FONT ", M. VILADEVALL *, A. CASAS * y R. VAQUER ** * Dpto. de Prospección Geológica y Geofísica. Fac. de Geología. Universidad de Barcelona. ** Dpto. de Petrología y Geoquímica. Fac. de Geología. Universidad de Barcelona. ABSTRACT A five year program of systematic multi-element geochemical exploration of the Catalonian Coastal Ran- ges has been initiated by the Geological Survey of Autonomic Government of Catalonia (Generalitat de Catalunya) and the Department of Geological and Geophysical Exploration (University of Barcelona). This paper reports the first stage results of this re- gional survey, covering an area of 530 km2 in the Mont- seny Mountains, NE of Barcelona (Spain). Stream sediments for metals and stream waters for fluoride were chosen because of the regional cha- racteristics. Four target areas for future tactic survey were recognized after the prospect. The most impor- tant is a 40 km* zone in the Canoves-Vilamajor area, with high base metal values accompanied by Cd, Ni, Co, As and Sb anomalies. Keywords: Catalanides. Geochemical exploration. Stream sediments. Base metal anomalies. Principal Component Analysis. RESUMEN En el marco de un convenio entre el Servei Geo- logic de la Generalitat de Catalunya y el Departamento de Prospección Geológica y Geofísica (Universidad de Barcelona), se ha emprendido un programa de explo- ración geoquímica multielemental en fase estratégica de las Cadenas Costeras Catalanas. El presente artícu- lo da cuenta de los primeros resultados de esta explo- ración de carácter regional. La primera zona estudia- da, cubriendo una extensión de 530 km*, corresponde al Macizo del Montseny (NE de Barcelona). Debido a las características fisiográficas de este macizo y en base a anteriores estudios de carácter local, se consideraron como idóneas la prospección de sedimentos aluviales para determinar los metales base e indicadores y la prospección hidrogeoquímica para determinar el flúor. Como resultado de esta cam- paña se han reconocido cuatro áreas con interés po- tencial para futuras prospecciones de carácter thctico, destacando una franja de unos 40 km2 en la zona Cá- noves-Vilamajor con valores anómalos de los metales base acompañados por Cd, Ni, Co, As y Sb. INTRODUCTION After the exploration of mineralisations in the NE of the Iberic Peninsula made during the period 1976-1980 (Viladevall, 1980), two rnairi regions for further strategic multi-ele- ment geochemical exploration were dehed: the Pyrinean and the Catalonian Coastal Ranges. This work was to be done in eooperation with the Geological Survey of the Autonomic Go- vernment of Catalonia, and began in 1981 (Font et al., 1983). The previous stage of the program was a me- thodologic search in a reduced arrea of the re- gion and as a result we found that stream se- diments and waters were the best materials for prospecting in such a Sasis. The first stage has been made in the Mont- seny Mountains, NE of Barcelona, covering an area of about 530 km2. The results of this study are presented here. GEOLOGICAL AND MINERALQGICAL FEATURES Montseny Mountains ccpmprise the Carnbro- Ordovician (gneisses, micaschists, marbles, sla- tes and shales), the Silurian-Devonian (shales, black shales, limestones and cherts) and the Carboniferous (shales, greywackes and cherts) metamorphosed to medium-grade and intruded by granitic andl porphiritic rocks of granodio- ritic to monzonitic-granitic composition and late Hercynian age (Viladevall, 1975; Casas, 1979; Julivert and Martinez, 1980). Triassic sediments cover the SW border and are built up of conglomerates, sandstones and clays of Buntsandstein facies. The Cenozoic contain marls, clay and sands- tone iil the NW and SE, filling up the Ebro and Valles depressions limited by NNE-SSW (IGME, 1976). Three main types of mineralisations can be distinguished (Font, 1983): 1) Magnetite-pyrrhotite or magnetite-sphaleri- te-scheelite (galena-chalcopyrite) skarns in the Cambro-Ordovician limestones. 2) Large F-Ba (Pb-Zn) veins and Pb-Zn (Ba) small veins associated to E-W faults. 3) Many veirilets of Ba trending NW-SE and NE-SW, and some veins of Cu, direction N-S. SAMPLING The physiographic features of the region (al- pine type), with a well-developed drainage system forming small basins, carried us to use stream sediments for metals and stream waters for fluoride on a strategic basis. Soils are scarce and shallow owing to steep slopes, hence they were not used at this stage. Sampling sites were chosen after an orientat- ion survey performed to determine the length of dispersion trains. The results of which indi- cates a sampling interval of 400-500 m for se- diments and 600-700 m for waters along the streams (Font, 1983). A total of 1069 stream se- diments and 790 stream waters were collected covering an area oE about 530 km2 (fig. 1). Samples were taken from the active stream channel, where posible, and no special attention was paid to seasonal variations of waters be- cause no significant (10-15 % ) differences were observed bef.ween dry and wet seasons. ANALYTICAL PROCEDURE Fluoride in waters The specific-ion electrode method has been used because of easy operation, high sensitivity (50 ppb in routine measures) and precision (bet- ter than 5 % relative). Samples and standards are mixed 1: 1 with TISAB (Total Ion Strength Absorptisn Buffer) and measurements made under standard cali- bration procedure between 0,l and 18 ppm. Stream sediments After drying, the minus 80 mesh fraction was used. Sample solution was performed with aqua regia (1 g. sample and 5 ml. of aqua re- gia), the final volume beeing 25 rnl. AAS flame measurements were made for Pb, Zn, Cu, Fe, Mn, Co, Ni, Cd and Ag with good (better than 5%) analytical preeision. Detection limits where satisfactory for all elements except Cd (2 ppm in stream sediments). Standards were corrected for Na, K and Ca (rnatrix ef- fect). Evaluation of the sampling error, sample treatment and analysis by flame AAS in dupli- cate samples gives deviations less than 20 94 relative. Most differences can be atributed to sample heterogeneities because physieal disper- sion seems to be dominant. Hydride-forming elements As, Sb and Hg were determined by AAS using sodium borohy- dride as a reductor. Analytical precision is bet: ter than 25 Y6 relative at low contents and bet- ter than 10 % at high concentrations. STATISTICAL TREATMEKT OF DATA For statistical purposes four different popu- lations related to main lithologies of the region were considered: slates of low metamorphic grade, granitic rocks, Triassic sandstoiles and Testiary marls. Univariate analysis Analisys of data distribution was made by constructing the frequency distributions and cumulative curves of the elements following the graphical procedure of Lepeltier (1969). The Figure 1.-Principal Components map of factor 1 (Pb - Zn - Cu - Ni - Cd - As). Factor scores are expressed in standard deviations. Figura l.- Mapa de los componentes principales del factor 1 (Pb - Zn - Cu - Ni - Cd - As). Las cargas facto- riales están expresadas en unidades de desviación estándard. TabPe 1. - Statlstical parameters sf main elements analyzed. Tabla l. - Parametros estadísticos de los principales elementos analizados. - - V) u u range .e 2-624 15-1125 1-146 2-925 1-140 0,2-5,3 0,03-5,P C mean 20,6 53,6 8;l 7 1,3 0,35 2 0,s st. dev. 3,75 1,6 2 3  2,1 1,1 1,6 3,1 range 10-815 18-2350 3-1485 8-138 1-35 0,2-5,3 0,2-120 2 mean <d 74 209 33 36 3,7 1 8,7 iij st. dev. 2,6 2 3  1 3  16,8 3,3 1,8 U U '3 range 8-55 10-108 3-30 8,30 1-2 0,2-3,4 0,3-9,2 1 mean 22,6 32,4 10,3 16,6 1,4 6 6  2,7 3 st. dev. 1,5 1,s 1,6 5,8 O S  2,1 1,8 range 10-595 10-975 1-125 3-50 1-5 0,2-2,3 0,2-38,2 % ZeYev. 42,4 83 16,3 25 1 3  0,6 4,3 Cc 2 2 2  2,7 14 1 2  1,9 2,6 ---normal or lognormal character of each element distribution was determined in the four litholo- gies. Background and threshold values were cal- culated afterwards (table 1). Four kinds of samples have been considered: -Background: between x and x+s or x, and Xg.Sg. - Possible anomaly: bettween x 9 S and x + 2s or x,.s, an,d x,.si. - Probable anomaly: between x+ 2s and x -+ 3s or x,.s: and x,.s;. - True anornaly: more than x+3s or than xg.s,3. Bi and Multivariate analyszs Correlation coefficient matrix and Principal Component Analysis have been made for each lithology. Tlhree factors explalning the 65-70 % of total variance were chosen. In each factor or component, loadings higher than 0.4 of the ele- nrents were considered significant. The factor or  component 1, called «mineralisation compo- nents is caimmsn to the four lithologies and comprises i:he elements association: Pb-Zn-Cu- Ni-CdAs (fig. 1). This cornponent must be as- ssciated ta mineralisations of skarn type or complex sulfide type (still unkown in the area). Compone:nt 2 and 3 are of rninor irnportance in this stage of the investigation, only compo- nent 2 in slates of low rnetarnorphic grade in- vslving Cu-Ag-Wg were considered. This csrn- ponent is possibly associated to copger veiqs known in the area, or rePated to the presence of black shales. From the recults of the statistical treatrnent of data some interesting points arise: - Pb and Zn are only significantly correlated in slates of low rnetrimorphic grade. Bsth elements shaw no enrichment in Fe and Nln oxides. - Ag and Pb are not associated in any lithology, having very low correlation coefficients. - Cu has a fairly good correlation with Ag and Hg only in pelitic paleozoic rnaterials. In the others lithologies, correlate well with Zn, Co, Ni and As. - Hg shows no general eorrelation wíth any element . CONCLUSIONS Four main target areas for future taetic sur- vey were recognized (fig. 1): 1) A 40 km2 zone of Zn, Pb and Cu high values, acompanied by Cd, Ni, CQ, As and Sb ano- malies in the .SW sf the prospeet. Rocks are pelites and limestsnes of Upper Ordo- vician to Carboniferous age. This geoche- mical association coincides with the first factor of Principal Component Analysis, explaining 41 % of total variance. 2) A group of Pb-Zn (Ag) and Co, Ni, Sb and As anomalies with moderate values occur In Triassic deposits at the NW of the Mont- seny (factors 1 and 2 of this lithology). 3) A conspicuous anomaly of Zn, Cu, Pb and Co at the SE associated with marbles and gneisses (skarn-type mineralisation) of Cambrian age. No statistical treatment could be made in skarns because of the small number of samples (34). 4) A strong anomaly of Hg of the SE and NW without apparent relation to target areas 2) and 3). There are severa1 scattered anomalies of F in water associated with fluorite-barite veins. REFERENCES CASAS, A. 1979: «Estudio litogeoquímico del Paleozoi- co del macizo del Montseny y su aplicación a la prospección minera». Tesis doctoral. 315 pp. Uni- versidad de Barcelona. FONT, X. 1983: «Estudio de las mineralizaciones del Macizo Montseny-Guilleries (Barcelona y Girona) y su aplicación en la prospección geoquimica de re- des de drenaje». Tesis doctoral. Universidad de Bar- celona. FONT, X.; VILADEVALL, M.; CASAS, A. and VAQUER, R. 1983: «Geochemical exploration in the Montseny Mountains, NE Spainn. 10th. IGES3red SMGP. Es- poo, Finland August 29 - September, 2, 1983. IGME. 1976: Mapa geológico de La Garriga. Escala 1 : 50.000. JULIVERT, M. and MARTYNEZ, F.J. 1980: «The Paleo- zoic of the Catalonian Coastal Ranges (North-wes- tern Mediterranean)». A'ewsletter, IGCP, 5 (2) 124- 128. LEPE]-TIER, C. 1969: «A simplified statistical treat- rnent of geochemical data by graphical represen- tationn. Econ. Geol., 64, 538-550. VILADEVALL, M. 1975: «Estudio petrológico y estruc- tural de las rocas metamórficas y graníticas del Sector Nororiental del macizo del Montseny (pro- vincias Barcelona y Girona)». Tesis doctoral. Uni- versidad de Barcelona. VILADEVALL, M. 1980: «Pasado, presente y futuro de la investigación y explotación de recursos natura- les no renovables en Catalunyan. Informe Servei Geologic de la Generalitat de Catalunya. 60 p. y 8 mapas. Inédito. Recibido: Septiembre 1984. 

Geochemical exploration in the Montseny Mountains (NE Spain)

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