Rock chemistry and fluid inclusion studies as exploration tools for ore deposits in the Sila batholith, southern Italy

Journal of GeochemicalExploration, 40 ( 1991 ) 291-310

291

Elsevier Science Publishers B.V., Amsterdam

Rock chemistry and fluid inclusion studies as exploration tools for ore deposits in the Sila batholith, southern Italy B. De Vivo a, R.A. Ayuso b, H.E. Belkin b, A. Lima a, A. Messina c and A. Viscardi ~ aDipartimento de Geofisica e Vulcanologia, Largo S. Marcellino 10, 80138 Napoli, Italy bU.S. Geological Survey, Reston, VA 22092, USA Clnstituto di Scienze della Terra, S. Agata--Papardo, 98166 Messina, Italy (Received December 10, 1989; revised and accepted June 26, 1990)

ABSTRACT De Vivo, B., Ayuso, R.A., Belkin, H.E., Lima, A., Messina, A. and Viscardi, A., 1991. Rock chemistry and fluid inclusion studies as exploration tools for ore deposits in the Sila batholith, southern Italy. In: A.W. Rose and P.M. Taufen (Editors), Geochemical Exploration 1989. J. Geochem. Explor., 40: 291-310. The Sila batholith is the focus of an extensive petrogenetic research program, which includes an assessment of its potential to host granite-related ore deposits. Univariate and multivariate statistical techniques were applied to major- and minor-element rock geochemical data. The analysis indicates that the highest potential for mineralization occurs in corundum-normative, peraluminous, unfoliated, relatively late-stage plutons. The plutons are enriched in Rb, Nb, Ta and U, but depleted in Fe, Mg and Sr. The K/Rb, Ba/Rb, Rb/Sr and Rb3/Ba-Sr.K indices and high R-factor scores of Si-K-Rb are typical of mineralized granitic rocks. A reconnaissance fluid inclusion study indicates that the sub-solidus rock was infiltrated by solutions of widely different temperatures (50-416 ° C) and variable satinities (0 to ~ 26 wt.% NaCI equivalent). The higher-temperature solutions probably represent granite or magmatic-related Hercynian fluids, whereas the lower-temperature fluids may be either Hercynian or Alpine in age. Fluids with characteristics typical of mineralized "porphyry" systems have not been recognized.

INTRODUCTION

The plutonic rocks of the Sila (Fig. 1 ) and Stilo Units, in addition to the plutonic rocks of the Aspromonte and Polia Copanello Units, were considered by De Vivo (1982) and Bonardi et al. (1982) as having the highest mineralization potential in the Calabria-Peloritani arc, southern Italy. The known mineral occurrences in the igneous rocks of the Sila Unit mainly consist ofZn, Pb, Cu, Fe and As sulfides. These were often associated with minor amounts of molybdenite and fluorite (see mineralization occurrence map in De Vivo, 1982). The most important of these occurrences are found as veins 0375-6742/91/$03.50

© 1991 - - Elsevier Science Publishers B.V.

292

~3. DE VlVO ET AL

% ~i

I ~J

LEGEINO

"I

,1

~' Po~

+7.+

15) 16)

"~ OKm

i

ROCK GEOCHEMISTRYAND FLUID INCLUSIONSTUD1ESOF ORE DEPOSITS,SILABATHOLITH,ITALY 293

in the granodiorites, along an E-W fracture system. This is particularly evident near Longobucco (Difesella del Trionto, LaManna and Macrocioli rivers), where there is evidence of ancient mining activity. Recent field work along the intrusive contact has resulted in the discovery of scheelite mineralization in the phyllites (RIMIN, unpublished data). A multi-element geochemical survey of active stream sediments within the Sila Unit area (De Vivo et al., 1981 ) indicated the existence of additional anomalous areas, in addition to those areas already known to host sulfide mineralization (around Longobucco, Cerenzia, Rossano). The most important of these lies east of Mt. Sordillo and west of Corigliano. A strong correlation exists between areas with known mineralization and the factor scores of the Pb-Zn-Cu and As-W-Be-Cu association. A more recent multi-element geochemical survey covering the entire Calabria-Peloritani arc (De Vivo et al., 1984) indicated anomalous areas in the Sila Unit on the basis of the Be-Sn factor scores and high residuals of Pb, Zn, Mo, As, Ba and Sn. De Vivo (1982) and Bonardi et al. ( 1982 ) attributed greater potential for mineralization to the occurrences in the Hercynian Sila and Stilo magmatic rocks relative to other areas in the Calabria-Peloritani arc because the Sila and Stilo plutons might have developed "porphyry Cu-Mo systems" that were fragmented during the Alpine evolution. These authors suggested that the development of such "porphyry systems" would be genetically related to a subduction zone formed during the evolution of calc-alkaline magmas of intermediate composition. Because regional geochemical studies in the Calabria-Peloritani arc (De Vivo et al., 1981, 1984) identified additional areas that might contain granite-related mineralization in the Sila and Stilo plutonic rocks, a more detailed multidisciplinary research program was developed. This program involves detailed mapping and rock sampling, petrographic studies, major- and minorelement chemistry by XRF and INAA techniques, 4 ° A r / a 9 A r thermochronological studies, fluid inclusion studies, and stable and radiogenic isotope determinations. This report concerns the Sila batholith and discusses the statisFig. I. Geological sketch map of the Sila nappe, Calabria, Southern Italy. Legend 2-12 = Sila Nappe and 3 - 1 0 = I n t r u s i v e rocks in the Sila Nappe, modified from Messina et al., in press: I - - m a i n l y clastic deposits of U p p e r Tortonian to Recent; 2 = Mesozoic to Tertiary sedimentary rocks; 3 = undifferentiated tonalite to granodiorite intrusions; 4=cordierite-bearing biotitemuscovite granodiorite to monzogranite; 5-- two-mica + andalusite + sillimanite Jr cordierite equigranular granodiorite; 6 = two-mica + andalusite + sillimanite medium to fine-grained granodiorite; 7 - - t w o - m i c a ÷ a n d a l u s i t e + sillimanite+cordierite inequigranular monzogranite; 8-- two-mica _+andalusite _+sillimanite +_cordierite equigranular monzogranite; 9 = two-mica _+ andalusite_+ sillimanite_+ cordierite inequigranular and medium-grained leucomonzogranite; 10 = smaller intrusions; 11 = low-grade metamorphic rocks; 12 = high-grade metamorphic rocks; 1 3 = l o w e r Alpine thrust nappes of the Sila Massif (Castagna, Bagni and ophiolitic Units)~ 14 = lower thrust contact of the Sila nappe; 15 = sampling sites; 16 = mineralization occurrences.

294

B. DE VIVO ET AL.

tical analysis of the major- and minor-element chemistry by univariate and multivariate techniques and a microthermometric and petrographic reconnaissance study of the fluid inclusions. Messina et al. (in press) have presented the petrographic observations and the major and minor element chemistry of the Sila batholith. A similar study of the Stilo (Serre) batholith is now in progress. THE PLUTONIC ROCKS

The calc-alkaline Sila batholith (600 km 2, Peacock index = 57 ) is the best studied Hercynian granite in Calabria. The batholith consists of shallowly emplaced, coalescing, nested, contemporaneous intrusives that range in composition from leucogabbro to peraluminous, corundum-normative, cordierite-, andalusite-, sillimanite- and muscovite-bearing leucomonzogranite, although tonalite and granodiorite predominate (Messina et al., in press) (Fig. 1). 4°Ar/39Ar age spectra from plutons within the Sila batholith document a single Hercynian emplacement and cooling history (about 300-270 Ma) with no evidence of later thermal effects (Sutter et al., 1988 ). Calc-alkaline modal variations include a tonalitic low-K trend in the sphene+ magnetite + allanitebearing rocks, and a medium-K trend in the granodiorites. Distinct modal variations distinguish the foliated (e.g., syntectonic tonalite ) intrusions from the massive (e.g., peraluminous) plutons, however, smooth and progressive variations in major and trace elements from least to most evolved rocks suggest they are chemically related. Trace-element variations (Messina et al., in press) in tonalites and granodiorites generally resemble those of plutons formed in orogenic margins (e.g., Rb = 100-150 ppm, Y + Nb = 30-45 ppm ). Peraluminous granites overlap chemical fields of plutons generated in orogenic and collisional settings (Rb> 150 ppm, Y + N b = 2 5 - 4 0 ppm). Rare earth element (REE) contents range widely in the batholith resulting in diverse light-REE enriched, chondrite-normalized patterns (Lacn=20-250, Ybc,= 1-20) with moderate to large negative Eu anomalies (Euc,= 1-30), and a relative depletion in heavy gEE (Lu~n= 2-5 ) that are characteristic of granitic rocks intruding thick continental basement. Many granites having the highest contents of heavy REE (LUcn= 5-30) have relatively fiat slopes for heavy REE (Tbc,/Yb~,= 1-1.2), and large negative Eu anomalies, and are found in the northern part of the batholith that hosts many of the mineralized veins. SAMPLING AND ANALYTICAL METHODS

Two hundred and fifty samples were obtained from the Sila plutons; however, the distribution of the samples reflects the scarcity of fresh rocks in areas of deep weathering.

ROCK GEOCHEMISTRY AND FLUID INCLUSION STUDIES OF ORE DEPOSITS, SILA BATHOLITH, ITALY 295

The major elements, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, La and Ce were analyzed in 142 representative samples by X-ray fluorescence; REE, SC, Cr, Co, As, Mo, Sb, Cs, Ta, Au, Th and U were analyzed in 69 selected samples by neutron activation (INAA). The data are given in Messina et al. (in press ). DATA PROCESSING

Univariate and multivariate computerized statistical techniques have been used for the interpretation of the large quantity of geochemical data. The data were converted to logarithms (base 10 ) prior to computations for factor analysis. The anomaly threshold was set at two standard deviations above the geometric mean ( g + 2tr), except for those elements with a normal distribuTABLE1 S u m m a r y statistics; arithmetic mean ( a ) , t h r e s h o l d s (a + 2tr ) and concentration range ( R ) of values ( * = geometric mean and geometric thresholds)

Elements

Mean ( a )

a+2o

Range ( R )

n = 142 SiO 2 A1203 Fe203 MnO K20 Ni* Cu* Zn Rb* Sr Y* Zr* Nh Ba La Ce

(wt.%) (wt.%) (wt.%) (wt.%) (wt.%) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)

65.36 15.78 1.37 0.07 3.48 7.5 4.1 89 129 218 25 159 14.6 752 37 73

79.71 18.42 4.40 0.18 5.80 31 33 217 256 451 63 436 29 1469 78 148

4 2 . 2 0 - 78.40 13.0018.60 0.018.22 0.020.30 0.416.85 2 . 5 - 105 1 - 251 13 - 606 5 - 320 16 - 803 8 - 125 16 - 532 5 - 85 29 -1793 1 - 129 6 - 236

n=69 Sc* Cr* Co* As* Mo* Sh Cs Ta* Th U* Au

(ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppb)

10.0 7.2 9.3 0.6 1.0 0.1 2.8 1.0 12.7 1.5 3.3

86 113 25 2.1 2.2 0.3 6.0 2.1 30.3 6.3 13.3

1.1 - 114 0.5 - 361 0.2 32 0.2 4.6 0.1 2.5 0.010.5 0.2 7.5 0.3 3.0 0.2 - 52 0.2 8.4 0.5 - 21

296

B. DE VlVO ET AL

S GIACOMQ OACR~

"1("

\

g

e,~e

LEGEND ®

~0,

>1842 %

0

Fe~ >440

(~

MnO >Q,18

0

K~ >580

(~

N, >31 ppm

I~

Co >25.0,,

0

Cu • 3 3 "

[]

As •

La • 78 pl)m ¢

.

Sc >86 0 a

Zn >217

(D

Ce • 1 4 8

Cr •113.0-

21 -

iVlo> 2.2

Rb >256

0

Sb>

03

Sr >451

~)

Cs>

60

p 0

Y

63

Ta>

21

.cAsrno

O

Zr >436

U>

63

)

0 "K"

•

Nb > 29

A

Th > 3 0 3

8a >1469

•

Au > 133 p ~

MINERALIZATION 0

2

4

OCCURRENCE 6

S

10 Km

ROCK GEOCHEMISTRY AND FLUID INCLUSION STUDIES OF ORE DEPOSITS, SILA BATHOLITH, ITALY

297

tion (Table 1 ). R-mode factor analysis (Davis, 1988 ), widely used in exploration geochemistry (e.g., Closs and Nichol, 1975; De Vivo et al., 1984), is an effective tool to reapportion the multi-element data into factors or elemental associations that characterize significant geological features. R-mode factor analysis has been computed on all the chemical data obtained for the 142 samples. In addition, in order to recognize plutons which may contain anomalously high values of Sn, W and Mo, the distribution of the K/Rb, Rb/Sr, Ba/Rb and the Rb3/Ba.Sr.K ratios has been used. These ratios are much more sensitive than the absolute enrichment distribution of elements in discriminating between barren and Sn-W-Mo-mineralized granitic rock (Govett and Atherden, 1988). RESULTS OF UNIVARIATE AND MULTIVARIATE STATISTICS

Only patterns of contiguous anomalous samples will be discussed in detail in the following sections. Figure 2 shows the distribution of the single-element anomalies. Anomalous samples are found in four areas: ( 1 ) The area surrounding Il Patire (northern sector) contains anomalies for Rb, Cs, Sr, Ta, U, Th, Ce, La, Ba, Nb and Au. This area also is characterized by late peraluminous plutons made up of two mica_ andalusite _+sillimanite_+cordierite granodiorite to leucomonzogranite (Messina et al., in press). Sulfide vein mineralization is found in this region (sphalerite, pyrite, chalcopyrite and galena). (2) The Longobucco area has anomalies for Sb, Fe and Zn. The main lithotypes of this area are cordierite-bearing biotite-muscovite granodiorite to monzogranite (Messina et al., in press); small-scale mining of vein mineralization containing sphalerite, with subordinate galena, pyrite, chalcopyrite and fluorite occurred in this area. Recently, scheelite mineralization has been found in the phyllites along the contact with the granitic rocks (RIMIN, unpublished data). (3) Northeast and east of S. Giovanni in Fiore, we have found anomalies for Mn, Y, Cr, Fe, As, Co, Cu, Ni and Sb, within tonalitic to granodioritic rocks, and within smaller intrusions of two-mica + andalusite_+ sillimanite _ cordierite granodiorite to leucomonzogranite (Messina et al., in press). This area also contains some molybdenite and other sulfide (vein) mineralization (galena, sphalerite, arsenopyrite, chalcopyrite ). (4) In the vicinity of Ampollino Lake, anomalies for Ni, Ba, Sr, La, K, Cu, Al, Fe, Zr, Y, Mn, Au, Mo and Sc have been identified. This area is characterFig. 2. Distribution of single-element anomalies in the Sila intrusive rocks. The numbers marking various lithologic units relate to the legend of Fig. I.

298

B. DE VlVO ET AL.

TABLE 2

Varimax-rotated factor matrix (six-factor model ) (n = 142 ). Loadings > P0.4tare underlined Elements

SiO2 AIzO3 Fe203 MnO KzO Ni Cu Zn Rb Sr Y Zr Nb Ba La Ce

Variance accounted % (total data)

Factors

Communality

1

2

3

4

5

6

0.8611 -0.8505 -0.3293 -0.7329 0.9032 -0.2779 -0.0450 -0.1862 0.8108 -0.6238 -0.2327 -0.4347 -0.0685 -0.0884 0.0936 -0.0077

0.0200 0.0401 -0.1022 -0.1669 0.0252 0.1323 -0.0928 0.0801 -0.3146 0.4897 -0.1810 0.6855 0.0119 0.7800 0.9266 0.9402

-0.1940 -0.0392 0.3862 0.1080 -0.1324 0.8482 0.9173 0.0220 -0.1155 0.2844 -0.1067 -0.0407 0.0055 -0.0329 0.0130 0.0221

-0.0654 0.0481 0.4173 0.0728 -0.0208 0.1535 -0.0963 0.0130 -0.0837 0.0115 -0.0181 0.0101 0.9764 0.0697 -0.0522 -0.0144

-0.1589 0.2847 0.1892 0.0759 -0.0079 -0.0432 0.0485 0.9497 0.0593 0.0302 -0.0147 0.2059 -0.0026 0.0507 -0.0301 -0.0149

-0.2703 0.1319 0.5443 0.5736 -0.1043 -0.0818 0.0612 0.0364 -0.0777 -0.2015 0.8827 -0.1241 0.0303 -0.2959 0.0225 -0.0147

40.02

26.08

12.10

8.30

7.06

6.44

0.882 0.827 0.774 0.917 0.845 0.846 0.868 0.945 0.786 0.751 0.878 0.718 0.959 0.712 0.872 0.885

ized by similar rocks as in S. Giovanni in Fiore (Messina et al., in press). No sulfide occurrences are known. A six-factor model, accounting for 84.17% of the data variability, was judged to be appropriate for the interpretation of the geochemical anomalies (Table 2 ). Elements with a factor loading greater than 0.4 or less than - 0 . 4 are considered to describe the composition of each factor. Figure 3 represents the distribution of the most representative association factor scores (Si-K-Rb), both in terms of lithology and known mineralization. The associations Si-K-Rb (with antipathetic AI-Sr-Mn-Zr) and La-Ba-CeZr-Sr, account for 40.02 and 26.08% of the total data variability, respectively. Clusters of very high scores for the association Si-K-Rb fall in the northern sector, around I1 Patire and correlate especially well with the known peraluminous plutons. Clusters of high factor scores for this association are also found in the area northwest and northeast of Cotronei and around S. Giovanni in Fiore, in association with tonalite to granodiorite, and with smaller intrusions of two-mica +_andalusite + sillimanite _+cordierite granodiorite to Fig. 3. Si-K-Rb association factor scores in the Sila intrusive rocks. The numbers marking various lithologic units relate to the legend of Fig. 1.

ROCK GEOCHEMISTRY AND FLUID INCLUSION STUDIES OF ORE DEPOSITS, SILA BATHOLITH, ITALY

~

os C_c~&IC 1O,

/~.....

4

+

.~r..~ucc:

.+>,~_.u @

\\

!

3

\

elN

_~

LEGEI~ ASSOCIATION FACTOR SCORES

IM0(~L 6)

SJ.K-Rb- (AI-SP-Mr~Zr)

~"

©

< -150

@

-

•

- O 7':~ ~ 0 3'5

O

0 75 te 150

•

.150

1.50to-075

MINERAUZAT~N C~JRRENCE

0

2

4

6

8

1OKra

0

I

-+-~_

r~O

o~

(

299

300

B. DE VIVO ET AL

~

",

\

"\

3

IU

\

\ I

s GI~A~t

IN FIORE

I I

LEGEND

KtRb

Barb

50t0150 []

O5Ot01.00 []

Rb'/(~.Sr.K

"~

> 7

0

1 to 7

0

> 0.100

•

0005 to O:lOOrl

MINERALIZATION OCCURRENCE 0

2

4

S

8.. ~Km

3

ROCK GEOCHEMISTRY AND FLUID INCLUSION STUDIES OF ORE DEPOSITS, SILA BATHOLITH, ITALY

301

leucomonzogranite. Another limited area with high factor scores occurs north of Mr. Carlomagno, within the same lithotypes of S. Giovanni in Fiore-Cotronei area. The association La-Ba-Ce-Zr-Sr shows one relevant cluster of very high factor scores in the area around Ampollino Lake. The combination of the high factor scores of the Si-K-Rb and La-Ba-Ce-ZrSr association complement the distribution of the single-element anomalies (Fig. 2 ) with the known lithology (Fig. 1 ). The other four associations (factors 3 through 6) consisting of Ni (Cu), Nb(Fe), Zn and Y(Fe-Mn) account for 12.10, 8.30, 7.06 and 6.44% of the total data variability, respectively. These behave essentially as single-element factors, although certainly Zn and Ni(Cu) are mineralization factors. Isolated high factor scores of these associations occur in the I1 Patire, Longobucco, Ampollino Lake and northeast of S. Giovanni in Fiore areas. Figure 4 shows the distribution of the significant K/Rb, Rb/Sr, Ba/Rb and Rb 3/Ba- Sr- K ratios. The "specialized" granitic rocks, porphyry granites and normal granites form a single series on the basis of the K/Rb and Rb/Sr ratios, but the "specialized" granites fall in a specific range with high Rb/Sr ( > 1 ) and low K/Rb ( < 150) (Govett and Atherden, 1988 ). Generally, from non-mineralized to mineralized rocks, there is an increase of Rb/Sr and a decrease of K/Rb. Govett ( 1983 ) points out that Sn-bearing granitoids may be recognized by high ratios of Rb/Sr and low ratios of K/Rb, Mg/Li and Ba/Rb. In addition, he suggests the use of the multiplicative ratio (Rb 3-L i ) / (Mg. Ba. Sr-K) as a discriminator between Sn granites and barren granites. We did not analyze for Li, thus we have modified the multiplicative ratio to Rb3/( Ba-Sr. K). Figure 4 shows that an area of high potential for Sn is around I1 Patire where "specialized" granitic rocks occur. These lithotypes account for the enrichment of granophile elements (e.g., Rb, REE, Ta, U, Th, Mo, F, Be, Nb), the higher content of SiO2 and K20 and the reduction ofgranophobe elements (e.g., Ba, Sr). A very significant result of the present study indicates that the late-stage unfoliated peraluminous intrusive rocks (Messina et al., in press) define areas of high potential for sulfide mineralization. The peraluminous rocks have high values of granophile elements and related high discriminator ratios. I1 Patire is the area of main interest. Other areas of interest are around Cotronei, the area between S. Giovanni in Fiore and Cerenzia, and the area north of Mr. Carlomagno (Fig. 4 ). FLUID INCLUSIONS

Type and distribution offluid inclusions Fluid inclusion data were obtained by microthermometric techniques on a calibrated Chaix-Meca heating and freezing stage (Poty et al., 1976 ). Heating Fig. 4. Distribution of the K / R b , Rb/Sr, Ba/Rb and Rb3/Ba-Sr-K ratios in the Sila intrusive rocks. The numbers marking various lithoiogic units relate to the legend of Fig. 1.

302

B. DE VIVO ETAL.

Fig. 5. Photomicrographs (plane-polarized transmitted illumination) showing representative types of fluid inclusionsin igneousquartz from Sila intrusive rocks. (A) Swarmsof intersecting trails of secondaryinclusions,bar scale= 50/~m. (B) Liquid-rich,type II, inclusions,bar scale= 10 /lm. (C) Liquid-rich, type II, inclusions and small (arrow) vapor-rich inclusions,type III, bar scale= 20/tm. rates of approximately 3 ° C / m i n were reduced to 1 ° C / m i n near the homogenization temperature. The uncertainty of the measurements is estimated to be +_3°C in the heating mode and _ 0 . 5 ° C in the freezing mode except as described below. All the measured fluid inclusions are hosted in magmatic quartz. Only 30 samples out of the 250 Sila granitoid samples contained inclusions amenable for measurement. We report 332 heating and 143 freezing measurements. All inclusions occur as swarms of intersecting trails (healed fractures) and thus are considered secondary (Fig. 5A). No daughter crystals or evidence of CO2 were observed. The fluid inclusions were classified by phase relationships observed at room temperature, according to the criteria of Nash (1976): type I inclusions (abundant), monophase (liquid) of low salinity; type II inclusions (abundant), (Fig. 5B,C ), liquid-rich, with salinities from low to very high; and type III inclusions (rare) (Fig. 5C ), vapor-rich (with undetermined salinity). The timing relationships between different inclusions trails are very difficult to decipher; generally, the type I monophase inclusion-rich trails are better defined than the type II two-phase liquid-rich inclusion trails suggesting that type I fluids may be later.

Composition offluids Unambiguous measurement of the initial melting temperatures (Te) was hindered by the small size of most inclusions ( < 15 a m ) . Quite often it was

ROCK GEOCHEMISTRY AND FLUID INCLUSION STUDIES OF ORE DEPOSITS, SILA BATHOLITH, ITALY

303

FELSIC DYKES LEUCOMONZOGRANITIC APLITE

0

2.0

40

60

8.0

10.0

120

14.0

16.0

18D

200

220

>23.0

Wt 96 NaCl equiv.

50

90

130

170

210

250

290

330

Th°C

Fig. 6. Histograms summarizing fluid inclusion salinity and homogenization temperature data grouped according to their provenance from the intrusive bodies of the Sila Unit, described by Messina et al. (in press).

only possible to establish an upper temperature limit at which melting was recognized. First melting temperatures range between - 3 0 and - 6 5 °C and indicate the presence of divalent cations other than Ca 2+. The measurements below - 50 ° C suggest that Zn 2÷ (ZnC12-H20, Te = - 62 ° C (Mylius and Dietz, 1965 ) ) or Fe 2+ (Crawford, 1981 ) are present. The final melting temperature ( Tm-ice) measurement was also hindered by the small inclusion size. In a few cases, when it was impossible to clearly detect the final melting temperature, the Tm-icewas estimated at the point where there was a sudden m o v e m e n t of the bubble in the inclusions. The salinities are expressed as equivalent weight % NaC1 and were determined from Tm-ice and the freezing point depression equations of Potter et al. ( 1978 ). The results shown in Figures 6-10 are grouped according to their provenance from the intrusive bodies described by Messina et al. (in press). Salinities calculated from final melting point measurements and reported as equivalent weight % concentrations of NaC1, are an approximation, particularly those for the higher-salinity fluids, where the presence of divalent cations in solution is suggested by the low Te values. The salinity ranges between 0 and near halite saturation ( ~ 26 wt.% NaC1 equiv. ).

304

B. DE VIVO ET AL.

MINOR INTRUSIONS

0

20

40

60

T W O MICA ± AND. ±SILL. t CORD MONZOGRANITE

T W O MICA *AND. * SILL GRANODIORITE

T W O MICA -+AND.-+SILL.*- CORD GRANOOIORITE

80 100 230 Wt%NaCI equiv

60

80 lOO 130

170

5L 5o

210 Wt %NaCI equiv.

°t,L

RR 70 ao

R 11o Wt%NaCI equiv

b~m

80

120 140 TWO

.................... ~ , , ~

110

150 190 2~0 270 3i0

350 Th°£ 110 150

190 230 270 Th°C

T W O MICAt AND.Z SILL.t CQIqD. EICOMONZOGRANITE

| 0"--~o 40 8o ~o ",a6:,,0"~-6~3o

T W O MICA t AND.-+ CORD. LEUCOMONZOGRANITE

50

7o

Wt% NaCI equlv

Wt % NaC~ equiv

°Lj

5Lo 80

12o

Th°C

Fig. 7. Minor intrusions. (For explanation see Fig. 6. ).

Heating data Homogenization temperatures ( Th ) of all the studied samples, grouped in to the intrusive bodies, are shown in Figs 6-10. The range o f homogenization temperatures is from 50 to 416 ° C. Although carefully checked, no type III inclusions were found to clearly homogenize in the vapor phase. Therefore, it was not possible to determine if the type III inclusions resulted from boiling or were formed by some postentrapment process (e.g., necking-down or intersecting fractures). Although "necked" inclusions were found in all samples; they were generally recognized and avoided. The Th measurements o f some inclusions were hindered

ROCK GEOCHEMISTRY AND FLUID INCLUSION STUDIES OF ORE DEPOSITS, SILA BATHOLITH, ITALY 3 0 5

POST TECTONIC MAIN INTRUSIONS

BLOT. AMPH.-TONALITE TO GRANOOIORITE

BlOT GRANODIORITE

1,~o " 16o " 18o " 260 Wt% hLgCtequi~

10

'LIo llo

!![!!T!!!!!

5

12'o "16'o " 260 "2,io 2 s o Th*C BLOT. TONALITE

T~

90

RA~OIORITE |

ii

|

15

130

170

... H ~ . . ~

o

=ll=

6 " 2b " 4b " 6b " elo 10o 12o Wt% NaCI equiv.

2o 40

210

250

370

•;410

o~c

i_~ CORD-BEARING BIOTqVIUSC. ~ R / ~ N O D I O R I T E TO MONZOGRANITE

100 ~

330

. ~ . n. r ~ . . H . n . . ~o eo ]oo 12o t4o 16.o Wt % NaCI equiv.

....~,~.,~. '-'::--':::-~::: I ~ I~

290

140

180

220

~. 260

300

Th°C

I~

"16o " ~ i o leo' a2o 260 Th°C 1.0

30

5.0

7.0

9.0

110

130

15.0

17.0

19.0

Wt %Na CI equiv.

Fig. 8. Post-tectonic main intrusions. (For explanation see Fig. 6. ). SYNTECTONIC MAIN INTRUSIONS AMPH. BEARING BIOTITE TONALITE

15

5

.

-

_.._~;.n

6.0

8.0

10.0 130 160

100

140

180

220

260

2i0 " Z30 Wt % Na CI equw.

300

340

Th°C

Fig. 9. Syntectonic main intrusions. (For explanation see Fig. 6. ).

306

B. DE VIVO ET AL.

SMALLER I N T R U S I O N S

T W O MICA ± AND.-+ SILL.-+ CORD LEUCOGRANODIORITE

40 so 60

.~,.~ 15o

Iso

Wt%NaCl

Th°C

equiv.

T W O MICA ± AND -+CORD LEUCOMONZOGRANITE

F~FI . . . ~ R I [ : : ] !

0 tO 20 30 40 50 SO 70 SO 9.0 100 W t % N a C I equiv.

5b 7b 9b lio ~ao '

Th°C

Fig. 10. Smaller intrusions. (For explanation see Fig. 6. ).

since the bubble near Th was not clearly visible during vapor/liquid homogenization. Repeated measurements on this type of inclusion gave homogenization temperatures reproducible within _+5 ° C. Also, because of the difficulty inherent in the small inclusion size, some of the Tm-ice (i.e. salinity) measurements may have been overestimated. The absence of data for the type III (vapor) inclusions precludes an analysis to determine if the coeval vapor-rich and liquid-rich inclusions satisfy the criteria for boiling (i.e., identical Th and salinities that are consistent with known PVTX data). Thus, for this study we have presented the data without a pressure correction. However, if we assume a trapping pressure (lithostatic) of 1.5 kbar, consistent with the shallow level of emplacement of the Sila granitoids, as indicated by petrographic evidence (miarolitic cavities), the homogenization temperatures (for non-boiling conditions ) would need a pressure correction of between 100 and 150°C (Brown, 1989). DISCUSSION

Origin of hydrothermal fluids and comparison with porphyry-typefluids The most important result of the preliminary fluid inclusion study is that we observed no primary, high-salinity, daughter crystal-bearing inclusions

ROCKGEOCHEMISTRYAND FLUIDINCLUSIONSTUDIESOF OREDEPOSITS,SILABATHOLITH,ITALY 307 25-

25~

A

B

20-

,•

20 -

13"

(D 15

(D 15-

o Z 10~

O Z 10-

I I

ii

~2

~

I

I

5-

5'0

1&o

i~o 2&o

Th

-W

~5o

s&o

:~o

°C

Oo

25q

~&o -i~;

Th ~&o°C

D

",

2Bo

3&o

35o

2;0

3&o

35o

25q

C •

•

go

20]

20-

II 0

O" ~15-

O ZIO.

O Z10

5

-

5 I

5'0

100

I

I

150

260

Th

°C

250

3(30

550

01o

~'o

~&o

~o Th

2do °C

25

20-

Z3 13"

015[3 Z~o

o~

i

II

5-

so

~&o

~o Th

2Co °C

2;0

;~o

35o

Fig. 1 I. Summary diagrams of homogenization temperature ( Th ° C) versus salinity data (wt.% NaCI Equiv. ), grouped according to their provenance from the intrusive bodies of the Sila Unit, described by Messina et al. (in press). (A) felsic dykes; (B) minor intrusions; (C) post-tectonic main intrusions; ( D ) syntectonic main intrusions; and (E) smaller intrusions.

308

B. DE VIVO ET AL.

characteristic of porphyry systems. These high-salinity brines together with evidence of boiling are thought to be the exsolution of an immiscible fluid directly from the crystallizing granitic magma (Roedder and Coombs, 1967) and would be likely to carry ore-forming species (Roedder, 1984). All observed inclusions were secondary and probably originated in a brittle-fracture regime from late-stage hydrothermal fluids and/or meteoric fluids. Homogenization temperature versus salinity data from the five groups of intrusions are shown in Figure 11 (A-E). The five diagrams show wide variations in fluid salinity and temperature, with data ranging from cool, dilute ( < 2 0 0 ° C and < 2 equiv, wt.% NaC1), to hot, saline fluids ( > 300°C and up to 26 wt.% NaCI equiv. ). Although the Th versus salinity data do not show any statistically significant trends that would help define their paragenesis, a geologically reasonable scenario would involve fluid mixing between ascending, hot saline fluids and cool, dilute meteoric waters (Hayba et al., 1985; Hedenquist and Henley, 1985 ). However, it would be very difficult to distinguish between the actual mixing of different fluids and the presence of different fluids at different times (i.e., Hercynian fluids versus Alpine fluids ). The argon closure temperature for microcline of 200°C obtained on the 4°Ar/39Ar isochron (300-200 Ma) (Sutter et al., 1988 ) represents an important constraint on the origin of the inclusion fluids. All inclusion fluids, which at the time of trapping, were > 200 ° C, must be Hercynian in age in order to perserve the known age relations. However, cooler fluids ( < 200 ° C; either dilute or saline) could be both Hercynian or younger (Alpine) in age. However, the most reasonable assumption is that the hotter, more saline fluids are related to the emplacement and cooling history of the Hercynian Sila intrusions and their attendant hydrothermal systems. CONCLUSIONS

Geographic grouping of anomalous samples, clusters of high R-mode factor scores, and field relations clearly indicate that some areas of the Sila batholith have potential as hosts of granite-related mineralization. Areas with the highest potential to contain sulfide mineralization (around I1 Patire, Longobucco, Ampollino Lake and northeast of S. Giovanni in Fiore) occur near corundum-normative peraluminous unfoliated intrusive bodies. These plutons are relatively enriched in Rb ( > 250 ppm), Nb ( > 29 ppm), Ta ( > 1.5 ppm), and U ( > 5 ppm), depleted in ferromagnesian elements and Sr, characteristically host sulfide-bearing veins, and have granite specialization indices ( K / Rb < 50; B/Rb <0.50; Rb/Sr >7; R b 3 / B a . S r . K >0.100) typical of granitic rocks hosting sulfide-rich veins. They are characterized particularly by clusters of high factor scores of the association Si-K-Rb and mineralization association [Zn, and N i ( C u ) ]. Fluid inclusions observed in the Sila plutons are not similar to those of

R O C K GEOCHEMISTRY A N D FLUID INCLUSION STUDIES OF ORE DEPOSITS, SILA BATHOLITH, ITALY

309

most mineralized porphyry systems but probably have formed in a brittlefracture regime as the result of episodic hydrofracturing. The fluid inclusions trapped at temperatures above the 4°Ar/39Ar microcline closure temperature (200°C), have been trapped during cooling of the Hercynian intrusions (300-270 Ma) (Sutter et al., 1988) after their emplacement, whereas the origin of the cooler ( < 200 °C) fluids is unknown. ACKNOWLEDGEMENTS

We are pleased to thank RIMIN, SpA for their cooperation. The research has been partially financed by M.P.I. (B.D.V.) and through a bilateral C.N.R. (Italia - U.S. Geological Survey) agreement. We also thank Jane M. Hammarstrom (USGS), Terry L. Klein (USGS) and two anonymous reviewers for their constructive reviews.

REFERENCES Bonardi, G., De Vivo, B., Giunta, G., Lima, A., Perrone, V. and Zuppetta, A., 1982. Mineralizzazioni delrarco Calabro-Peloritano. Ipotesi genetiche e quadro evolutivo. Boll. Soc. Geol. Ital., 101: 141-155. Brown, P.E., 1989. FLINCOR: A fluid inclusion data reduction and exploration program. Second Biennial Pan-American Conf. on Research on Fluid Inclusions, Program, with Abstr., p. 14. Closs, L.G. and Nichol, I., 1975. The role of factor and regression analysis in the interpretation of geochemical reconnaissance data. Can. J. Earth Sci., 12 (8): 1316-1330. Crawford, M.L., 1981. Phase equilibria in aqueous fluid inclusions, Mineral. Assoc. Can. Short Course Handb., 6: 75-100. Davis, S.C., 1988. Statistics and Data Analysis in Geology. Wiley, New York, NY, 646 pp. De Vivo, B., 1982. Mineral resources of the Calabria-Peloritani Arc: Genetic aspects in the evolution of the arc. Earth Evol. Sci., 3: 187-196. De Vivo, B., Cavaliere, S., Lima, A. and Crisci, G.M., 1981. Active stream sediments multielemental geochemical survey in the Longobucco area (Calabria). Boll. Soc. Geol. Ital., 100: 499-525. De Vivo, B., Closs, L.G., Lima, A., Marmolino, R. and Perrone, V., 1984. Regional geochemical prospecting in Calabria, Southern Italy. J. Geochem. Explor., 21:291-310. Govett, G.J.S., 1983. Geochemistry in Mineral Exploration. Elsevier, Amsterdam, 461 pp. Govett, G.J.S. and Atherden, P.R., 1988. Applications of rock geochemistry to productive plutons and volcanic sequences. J. Geochem. Explor., 30: 223-242. Hayba, D.O., Bethke, P.M. and Foley, N.K., 1985. Geologic, mineralogic, and geochemical characteristics of volcanic-hosted epithermal precious-metal deposits. Rev. Econ. Geol., 2: 129-167. Hedenquist, J.W. and Henley, R.W., 1985. The importance of CO2 on freezing point measurements of fluid inclusions: Evidence from active geothermal systems and implications for epithermal ore deposits. Econ. Geol., 80:1379-1406. Messina, A., Barbieri, M., Compagnoni, R., De Vivo, B., Perrone, V., Russo, S. and Scott, B., in press. Geological and petrochemical study of the Sila nappe granitoids (Northern Calabria, Italy). Boll. Soc. Geol. Ital.

310

s. DE VlVOETAL.

Mylius, J.L. and Dietz, N., 1965. Solubility of zinc chloride (ZnC12) in water. In: W.F. Linke (Editor), Solubilities of Inorganic and Metal Organic Compounds, 4th ed. Am. Chem. Soc., 2: 892. Nash, J.T., 1976. Fluid inclusion petrology-data from porphyry copper deposits and application to exploration. U.S. Geol. Surv. Prof. Pap. 907-D, 16 pp. Potter, R.W., II, Clynne, M.A. and Brown, D.L., 1978. Freezing point depression of aqueous sodium chloride solutions. Econ. Geol., 73: 284-285. Poty, B., Leroy, J. and Jachimowicz, L., 1976. Un nouvel appareil pour la measure des temperatures sous le microscope; l'installation de microthermometrie Chaix Meca. Soc. Fr. Mineral. Cristall. Bull., 99: 182-186. Roedder, E., 1984. Fluid inclusions. Rev. Mineral., 12, 646 pp. Roedder, E. and Coombs, D.S., 1967. Immiscibility in granitic melts indicated by fluid inclusions in ejected granite blocks from Ascension Island. J. Petrol., 8:417-451. Sutter, J.F., Messina, A. and De Vivo, B., 1988.4°Ar/39Ar thermal history ofHercynian plutons in northern Calabria (Sila), Southern Italy. Geol. Soc. Am. Meeting, Denver, Abstr., p. A165.