Jan 14, 1988 - position of six S-containing springs in Latium includ- ing Acque Albule ...... ira ciclo carsico c circuito idrotermale nella Pianura Pon- tina (Lazio ...
Applied Geochemistry. Vol. 3, pp. 475-486, 1988
0883-2'~27/88$3.00 + .DO P,~rgamonPress plc
Printed in Great Britain
Isotopic and chemical assessment of geothermal potential of the Coili Albani area, Latium region, Italy W . F. GIGGENBACH Chemistry Division, DSIR, Private Bag, Petone, New Zealand A . A . MINISSALE C.N.R. Centro di Studi per la Mineralogia e la Geochimica dei Sedimenti, Via G. La Pira 4, 50121, Firenze, Italy
and G.
SCANDIFFIO
ENEL Unita' Nazionale Geotermica, Via A. Pisano 120, 56100, Pisa, Italy (Received 14 January 1988; accepted in revised form 28 March 1988)
The chemical and isotopic compositions of low-temperature mineral waters discharged over the Colli Albani region (south of Rome, Italy) are those of highly immature waters of essentiallymeteoric origin formed through absorption of gases emanating from greater depth, followed by cation leaching of country rock at shallow levels. The composition of the gases discharged points to the presence, at depth, of a CO2-producing high temperature system in its waning stage. Low H2 and unsaturated hydrocarbon contents, as well as relative He, Ar and N2 contents indicate long residence time for the rising gas phase of the order of 1 Ma. On the basis of these findings, temperatures higher than 120°C appear unlikely to exist at shallow depth. Abstract
INTRODUCTION
(2 g/l) group of Ca-SO4-HCO3 waters disvolcanism (Fig. 1). It is part of a geological setting charged from a limited number of springs to the north typical of most of central Italy, where a Mesozoic of the Colli Albani. They concluded that the first carbonate suhstrate, generally acting as a geothermal group were waters of shallow circulation in contact reservoir, underlies shaly Mesozoic/Cenozoic with volcanic rocks of the Colli Albani complex, allochthonous units and clastic Neogene formations unaffected by fluids possibly present at greater depth. accumulated in continental and marine basins formed The chemistry of the second group of waters was after the Tortonian tectonic phase. Sometimes, as in explained in terms of slow circulation within a karstic the case of Colli Albani, they are overlain by a aquifer providing exposure to sedimentary carbonvolcanic cover increasing in thickness towards their ates and evaporitic sulfates at comparatively low source. The Colli Albani are dormant volcanoes, temperatures (
