Porphyry Copper Ore Research Articles

Sulfur evolution of oxidized arc magmas as recorded in apatite from a porphyry copper batholith

Uniformly sulfur-rich cores abruptly zoned to sulfur-poor rims (∼1 to <0.2 wt% SO3) in apatite from the Yerington batholith, Nevada, indicate that early magma that is crystal poor, oxidizing, and sulfate rich evolved to sulfate-poor magma via crystallization of anhydrite, a mineral observed in magmas from Pinatubo and El Chichon. We predict that the characteristic zonation to sulfur-poor rims of apatite in the Yerington batholith is common in other oxidized, hydrous, calc-alkaline magmas, and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution. Sulfate-rich arc magmas such as Yerington magmas may crystallize to produce hydrothermal fluids rich in chlorine, copper, and sulfur and porphyry copper ores.

40 Ar/ 39 Ar geochronology of Cu-Au and Au-Ag mineralization in the Potrerillos District, Chile

High resolution 40 Ar/ 39 Ar dating of porphyry stocks and related hydrothermal minerals from porphyry copper and epithermal precious metal deposits in the Potrerillos district of Chile demonstrates the very short duration of hydrothermal activity in these ore-forming systems. Ages of primary magmatic phenocrysts and hydrothermal alteration minerals in seven distinct intrusive centers show that individual porphyry stocks and their hydrothermal systems formed in very brief episodes, within a period of igneous activity lasting at least 8 m.y. during late Eocene through early Oligocene time. During this period of igneous activity, porphyry stocks that produced classic porphyry copper ore and porphyry-related epithermal gold ore were emplaced intermittently with barren porphyry stocks.At the Cobre porphyry copper deposit, 40 Ar/ 39 Ar ages of fresh hornblende phenocrysts (35.87 + or - 0.21 Ma), primary and secondary biotite (35.65 + or - 0.03 Ma), and sericite from late-stage vein envelopes (35.64 + or - 0.03 Ma) suggest that this hydrothermal system cooled from hornblende argon closure temperature (ca. 570 degrees C) to biotite closure (ca. 300 degrees C) in about 230,000 yr or less. At the smaller Norte porphyry copper deposit, ages of hornblende phenocrysts (36.76 + or - 0.20 Ma) and plagioclase phenocrysts (36.64 + or - 0.08 Ma) suggest that this porphyry stock and its hydrothermal system cooled below the plagioclase argon closure temperature (ca. 250 degrees C) in 120,000 yr or less.Magmatic biotite (40.82 + or - 0.19 Ma) in a porphyry stock that is spatially associated with the El Hueso epithermal gold deposit and hydrothermal sericite (40.25 + or - 0.05 Ma) from gold-bearing quartz veinlets in porphyry at El Hueso are 5 m.y. older than the Cobre porphyry copper deposit. This result contradicts previous claims of a genetic link between the El Hueso and Cobre deposits but supports a genetic link between epithermal- and porphyry-type deposits in the district. The age of coarse-grained alunite (36.23 + or - 0.08 Ma) associated with diaspore, pyrophyllite, dickite, and zunyite demonstrates that advanced argillic alteration adjacent to the epithermal deposit significantly postdated Au mineralization there, attesting to the superimposition of a second hydrothermal system at El Hueso. The heat source that drove this younger hydrothermal system has not been identified.A barren porphyry stock (Bochinche, 37.91 + or - 0.06 Ma) is the only porphyry in the district that has known cogenetic volcanic deposits. This barren stock was emplaced after the Gonzalez copper porphyry (38.85 + or - 0.06 Ma) and before the Norte copper porphyry. Like the mineralized porphyries, dating shows that the Bochinche porphyry cooled very rapidly (within 90,000 yr) from hornblende argon closure temperature to below the argon closure temperatures of biotite and plagioclase (250 degrees -300 degrees C). Two other barren porphyry stocks, Cerro El Hueso (33.13 + or - 0.06 Ma) and Cuesta (32.56 + or - 1.80 Ma), have no known related volcanic rocks.Numerical modeling of conductive heat flow in a shallowly emplaced, 500-m-wide porphyry stock shows that it would cool below the argon closure temperature of all datable minerals in less than 40,000 yr; hydrothermal circulation would shorten this time span. This result suggests that the duration of many ore-forming, porphyry-related hydrothermal systems is not resolvable by the best available geochronologic methods unless hydrothermal activity has been prolonged by multiple, spatially coincident intrusive events.

Flotation behaviour of gold during processing of porphyry copper-gold ores and refractory gold-bearing sulphides

Porphyry copper ores and gold-bearing sulphides are significant contributors to overall world gold production. Flotation is the principal process for pre-concentration of the sulphides, for subsequent smelting, roasting or hydrometallurgical treatment. Lakefield Research has had the opportunity to study ores from many large deposits, both new discoveries and existing operations. Research was aimed at improved metal recoveries by applying new concepts in flowsheet design or by introducing more specific flotation reagents. This paper highlights the variability of porphyry copper deposits that have been tested and suggests mineral processing techniques that can be used to overcome the effects posed by the different ore matrices. Some of the innovative flotation practices are discussed.

The Precordilleran fault system of Chuquicamata, Northern Chile: evidence for reversals along arc-parallel strike-slip faults

The Chilean Precordillera, situated between the Longitudinal Valley and the Western Cordillera of Northern Chile, was the site of the Andean magmatic arc from the late Cretaceous to the Eocene-Oligocene boundary. Magmatism came to an end during the Incaic tectonic phase (38 Ma), which caused arc-normal shortening and the development of longitudinal dextral strike-slip faults (Precordilleran Fault System). This magmatic arc tectonism is also related to the formation of the Chuqicamata porphyry copper ore deposit as well as of other important deposits of this type in the Precordillera. Structural investigations in and around the Chuqicamata open-pit mine have shown that wrench tectonics determined the kinematics of the area. The NS-striking West Fissure, which separates a 35-Ma-old non-mineralised pluton to the west from a central late Paleozoic basement ridge containing the mineralization, became a sinistral fault along with other parallel faults in the area. The central part is separated from similar Paleozoic rocks to the east by the Messabi-Este fault and a narrow faulted and sheared syncline of Mesozoic-Cenozoic sediments. This fault bears structures indicating dextral movements, which probably are of an age that is similar to the mylonites (34.8 Ma) in the western pluton. The dextral movements preceded the sinistral shear. Thus, the fault system of Chuqicamata displays a reversal of arc-parallel shear movements. According to the orientation of quartz veins in the mineralized body, it is presumed that the sense of displacement of these strike-slip motions reversed, when mineralization started at about 32 Ma. During this time the stress field must have changed fundamentally. The Incaic Phase dextral transpression is supposed to have been induced by the oblique vector of plate motion. The following sinistral transtension corresponds to a time of reduced convergence rate and possibly reduced plate coupling. As, however, the vector of plate motion remained unchanged during that time, oblique subduction cannot be used as an argument for arc-parallel sinistral shear movements.

Comparison of methods used to inhibit bacterial activity in sulfide ore bioleaching studies

Eight methods of ore sterilization, including steam autoclaving, dry heat, tyndallization, cobalt-60 irradiation, thymol (5-methyl-2-(1-methylethyl) phenol) and mercuric chloride additions, were tested using a monzonite porphyry copper ore containing chalcocite, chalcopyrite, pyrite, and minor molybdenite. All treatments were found to effectively eliminate iron-oxidizing bacteria added to the ore. Heating methods were found to be effective sterilization procedures and to have a minimal influence on the leaching characteristics of the ore. However, gamma irradiation and the additions of thymol and mercuric chloride significantly altered the ore and suppressed the abiotic leaching rate. Results suggest that previous bioleaching studies using thymol as a bacterial inhibitor may have overestimated the bacterial role in ore leaching.

In-line static mixer rapid flotation system for improved flotation kinetics

The US Bureau of Mines investigated rapid froth flotation through more efficient bubble-particle collisions that improved the overall flotation kinetics. An in-line static mixer efficiently mixed the bubbles, water and ore, selectively attaching these bubbles to the hydrophobic mineral’s surface. As the mixture entered the flotation chamber, the hydrophobic mineral was already attached to the bubbles and was quickly floated away from the remaining ore pulp. The rapid flotation system was evaluated for beneficiation with a western porphyry copper ore containing 0.67% copper and with a phosphate-bearing amine flotation tailings sample containing 9.5% P2O5 in a quartz matrix. Over 88% of the copper was recovered from the ore in a rougher concentrate containing 5.9% copper at a rate seven times faster than conventional flotation. Sixty percent of the quartz in the phosphate-bearing sample was floated at a rate four times faster than conventional flotation. The unfloated product retained 80% of the phosphate in a 16.9% P2O5 concentrate.

Exploring the ultrasonic comminution of copper ores

This paper presents grinding results obtained with a Chilean porphyry copper ore in the ultrasonic nip roll grinder of the US Comminution Center. Comparison with ball milling is performed by scaling-down industrial ball mill behavior to the ultrasonic grinding conditions. For small gap setting in the ultrasonic device, size distribution and specific energy consumption are in the same order of magnitude for both alternatives, but for larger openings in this ultrasonic prototype, the ball mill is much more efficient. Current design of the ultrasonic device is analysed and reasons why oversize and undersize particles are not well fractured are discussed. In spite of the current limitations, it is concluded that there is great potential to improve its performance.

Structural evidence of orogen-parallel strike slip displacements in the Precordillera of northern Chile

The Chilean Precordillera, situated between the Longitudinal Valley and the Western Cordillera of northern Chile, is made up of several elongate basement ridges following the trend of the Andes. These ridges, which morphologically rise above the Mesozoic-Tertiary cover rocks, are developed as anticlinal cores or as pressure ridges bounded by reverse faults and, thus, show considerable orogennormal shortening. Several nearly vertical faults cut through the Precordillera, parallel or at a very low angle to the mountain ranges. From the following structures it can be inferred that orogen-parallel transcurrent movements took place along the faults: (a) asymmetric en echelon fault arrays, (b) stratigraphic and structural discontinuities across major faults, (c) fabrics in fault rocks, and (d) vertical folds. A dextral displacement of the order of tens of km is probable. The orogen-parallel strikeslip movements as well as the orogen-normal shortening are considered as phenomena of magmatic arc tectonics due to the focussing of central Andean igneous activity on the Precordillera from the Late Cretaceous until the paroxysm of deformation (45-30 Ma). Deformation along the Precordilleran Fault System is related with the development of the large porphyry copper ore deposits of that area. The structural evolution of the Precordillera can be explained by oblique subduction resulting in dextral transpression.

On the Yangtze-type copper deposits and their polygenetic origin

The so-called “Yangtze-type” copper deposits include: (1) Cu-bearing massive pyrite bed, (2) Cu-bearing skarn and magnetite-type ore deposits, with replacement Cu-vein-type deposits near the metasomatic zone, and (3) mineralized intrusive bodies and breccia pipes, some of which are known as porphyry copper ores (e. g. Chengmenshan). This type of ore deposits is a typical example to verify the polygenesis of most of the deposits in China, as has been promoted by Prof. Tu Guangchi in view of the polycyclic development of the geological history in China. This paper is concerned with one sub-type of such deposits.

Bias in the analysis of geological materials for gold using current methods

Abstract A consistent pattern has been observed in the results obtained for Au in three soil and two porphyry copper ore samples serving as control reference standards in geochemical analyses. The mean reported by wet chemical methods (regardless of the measurement technique) was less than the mean by fire assay-based methods which, in turn, was less than the mean reported by laboratories using direct instrumental neutron activation analysis (INAA). These data have been obtained from 16 laboratories, some employing more than one method. Compared to INAA, values obtained for Au (at the 30–300 ppb level) using aqua regia (AR) dissolution were low by 24–42%, while those reported by fire assay-based methods were low by 14–26%. Studies of these samples and 32 rocks of widely varying composition revealed that the amount of Au remaining in the residue after AR attack ranged from 4% to 59% of the total. Gold dissolved by AR was determined by graphite furnace atomic absorption spectrometry (GFAAS) after extraction into MIBK (methyl isobutyl ketone), whereas Au remaining in the residue was determined by INAA. The slope of the line obtained by plotting Au by INAA vs. the sum of Au by AR/GFAAS and Au in the residue was not significantly different from 1.0. Modifications to the AR procedure such as prior attack by HCl or HF did not improve the recovery of Au in the three reference soils. However, reduction of sample size from 10 g to 1 g while maintaining the volume of AR at about 30 ml did increase results for Au. Furthermore, addition of HF in the attack on 1-g samples yielded results virtually identical to those obtained by INAA. It is thought that the poor extraction efficiency by AR is due to non-wetting of the larger sized sample, a lack of intimate, prolonged contact between the grains of the sample and the acid mixture and the presence of insoluble gangue surrounding Au particles. Constant agitation of the sample during evaporation with AR is desirable. The mean values obtained for Au in the soils by fire assay methods were not significantly different from the results by INAA (low by 14–19%); this was not the case for the two copper ore samples (low by 26%). This probably reflects the difficulties encountered in fire assay by high concentrations of Cu which hinder effective collection and separation of Au into the Pb button. However, the accuracy of the INAA method has not been established and is dependent upon measurement procedures and the degree of certainty associated with the Au values assumed for the reference materials employed for calibration. While estimation of precision does not present a problem, accuracy is difficult to assess in the absence of certified reference materials for Au at concentrations in the 10–300 ppb range. However, it is concluded that methods based upon AR dissolution can lead to low results, the magnitude being dependent upon the sample matrix and the mineralogical association of the Au present.

The interaction of flotation chemistry and size reduction in the recovery of a porphyry copper ore

In the industrial-scale processing of low grade porphyry copper ores, the cost of size reduction represents the major capital and operating expense item. The goal of grinding is to achieve a small enough particle size range of the feed ore so that valuable minerals are sufficiently liberated from undesired gangue enabling the process of flotation to be efficiently used. The purpose of this paper is to demonstrate that the proper choice and use of flotation reagents, especially of the frother, can help significantly in reducing the amount of grinding required per ton of feed ore and yet maintain reasonable mineral recovery from flotation. This is achieved by using specific types of frother chemistry which enhance the recovery of coarser and partially liberated mineral particles over normal practice. A related benefit to enhanced coarse particle flotation is the minimization of mineral recovery losses associated with fine (slime) particles.

Petrology of the Yerington Batholith, Nevada; evidence for evolution of porphyry copper ore fluids

The Jurassic Yerington batholith, western Nevada, is a composite pluton that contains several centers of porphyry copper mineralization and is exposed in structural cross section at paleodepths ranging from 0 to 8 km. Within these exposures the McLeod Hill quartz monzodiorite, Bear quartz monzonite, and Luhr Hill granite form successive intrusions that are in turn volumetrically smaller ( approximately 75, 19, and 6 vol %, respectively), more deeply emplaced (tops at 65-km 3 Luhr Hill granite. The low Cu content ( approximately 10 ppm) of the granite would allow extraction of approximately 50 ppm Cu from it during crystallization. These data suggest an orthomagmatic model in which both high- and low-density saline aqueous fluids formed during exsolution of water from the crystallizing Luhr Hill granite; and from which salts, Cu, Fe, and S strongly partitioned into the high-density fluid. Low-density fluids may have risen from the magma as a vapor plume. Mineralization occurred when fluid overpressures caused fracturing of wall rock and upward intrusion of granite porphyry dikes and high-density saline ore fluids. Both the f (sub O 2 ) path during subsolidus cooling and the deposition of most S as chalcopyrite-pyrite in ore suggest that reduction of magmatic S to sulfide may have been a mechanism for oxidation of magmatic ferromagnesian silicate and Fe-Ti oxide minerals.

Nd and Sr isotope study of hydrothermally altered granite at San Manuel, Arizona; implications for element migration paths during the formation of porphyry copper ore deposits

A study of the Nd and Sr isotope composition of the Late Cretaceous monzogranite stock at San Manuel, Arizona, and its mineralized alteration halo was undertaken in order to assess the transport of Nd and Sr that accompanied the hydrothermal alteration. Sampling was along a 1-km transect perpendicular to the alteration zones extending from the potassically altered core to the propylitically altered fringe of the system. Large isotopic differences between the stock and the enclosing 1.4-b.y.-old granitic wall rock, coupled with the original homogeneity of the latter, provide optimal conditions for detecting evidence of chemical transport. The mineralizing porphyry stock has a lower 87 Sr/ 86 Sr ratios (0.708) and a higher epsilon Nd (-6) than the Precambrian granite wall rock (0.782, -11). The 87 Sr/ 86 Sr ratios of the altered wall rock decrease regularly from 0.782 to 0.715 from the propylitic alteration zone to the stock contact, indicating that material flow was primarily from the stock into the wall rock, consistent with an orthomagmatic model for porphyry copper ore genesis. The Sr in the ore zone is 75 percent stock derived, and evidence of stock-derived Sr is found up to 700 m into the wall rock. The Sr and Rb concentration variations are mainly controlled by the alteration mineralogy and do not correlate with the isotopic variations. The epsilon Nd values and the Sm and Nd concentrations of the altered wall rock show subtle changes that are mostly confined to the potassically altered zone. Only one wall-rock sample, located 0.5 m from the stock contact, is strongly disturbed. The results suggest that Sr isotopes may provide a useful tool for studying or locating fossil hydrothermal systems, whereas the relatively immobile Nd isotopes are reliable indicators of the magmatic provenance of altered intrusions.

Island Copper grinding circuit — a progress review

The semiautogenous grinding circuit at the Utah Mines Ltd., Island Copper operation, located on Vancouver Island, British Columbia, is described. Since startup of the operation in 1971, grinding circuit throughput has been progressively increased from the initial design rate of 30 000 (33,000) to the current average 45 000 t/d (49,600 stpd) of porphyry copper ore. Key developments and modifications in operating and maintenance practice that have contributed to this increase are reviewed.

Model Discrimination in the Flotation of a Porphyry Copper Ore

Numerous flotation models have been proposed in the literature. Thirteen of these have been applied to batch flotation data and evaluated with respect to one another using statistical techniques. Flotation tests were carried out on samples of a US porphyry copper ore (Pinto Valley, AZ). The ore was tested using various collector and frother systems to produce different time-recovery profiles. These were used to calculate flotation rate and ultimate recovery parameters for each model. The models were then evaluated statistically to determine the overall fit of the calculated to the observed data and to test the range of significance of the parameters in each model.

Factors affecting the flotation recovery of molybdenite from porphyry copper ores

Investigations have been conducted to characterize the surface chemical and flotation properties of molybdenite in aqueous environments typical of those that exist in the copper circuits of plants which process porphyry copper ores. These investigations have revealed that molybdenite and quartz particles are negatively charged at the pH commonly used for bulk sulfide flotation, namely 11. While the adsorption of calcium ions reduces the magnitude of negative charge on molybdenite, the adsorption can reverse the surface charge on quartz particles when the calcium concentration in solution exceeds 1 × 10 −3 M. Heterocoagulation of molybdenite and quartz particles will thus be inevitable in solutions containing large amounts of lime and will impair the floatability of molybdenite. The deleterious effects of heterocoagulation can be somewhat overcome by an ultrasonic conditioning prior to flotation. Besides heterocoagulation, particle size is very critical for optimum molybdenite flotation. Coarse molybdenite particles (120 × 200 mesh) float extremely rapidly and completely without being influenced by heterocoagulation. The flotation of fine molybdenite particles (minus 200 mesh) is sensitive to particle size and heterocoagulation. Results of tests conducted to assess the effects of overgrinding of molybdenite have indicated that while there is no change in the crystal structure due to prolonged grinding, the floatability is significantly reduced due to the creation of very rough surfaces.

Geochronology of the porphyry copper deposits and related mineralization of Mexico

K–Ar dating demonstrates that all but eight of 41 dated porphyry copper and related ore deposits of Mexico were emplaced during the Laramide episode of maximum plate convergence. One older deposit is related to the Jurassic volcanic arc of western North America, one is pre-Laramide Cretaceous, four are Oligocene in age, and two late Cenozoic deposits are within the modern trans-Mexican–Chiapenecan volcanic arc. Thirty-three of the deposits lie within a long narrow belt that continues into Arizona and New Mexico, and widens from 100 km to over 300 km in the region of maximum extension in the southern Basin and Range Province. Eighty-five percent of the deposits were emplaced during the eastward transgression of the Cordilleran volcanic arc in middle Cretaceous through Eocene time.The occurrence of the porphyry copper deposits of Mexico appears to be independent of the terrane intruded and the copper content of the wall rocks where the wall rocks predate the volcanic arc, which is syngenetic with the porphyry stock. However, strontium is significantly more radiogenic where the host porphyry has intruded terrane having a Precambrian crystalline basement. Most frequently, the porphyry pluton can be observed to have intruded penecontemporaneous volcanic rocks or the batholith itself. The porphyries appear to be apophyses of the batholiths. The relationships suggest that the ore components are contained within the calc-alkaline batholiths and concentrated in the subvolcanic porphyries and wall rocks during transport of hydrothermal fluids to the volcanic orifice.The shape of the Cordilleran copper belt is controlled by magma composition, existence of a protective capping of dominantly volcanic rock, uplift, time, and erosion. As the continental volcanic arc that produced the porphyry copper deposits progressed eastward, the associated magma became more alkalic and copper poor. Thus, enrichment to ore grade became increasingly improbable to the east. Uplift and ample time for erosion prior to the return of the continental volcanic arc reduced the probability of ore preservation to the west. Optimum conditions for preservation were present within the belt where burial of calc-alkalic porphyry plutons under a thick volcanic cover occurred before removal of the ore zone by erosion. The broader width of the porphyry belt to the north is probably the result of both more extensive basin-and-range extension and basin-and-range taphrogeny that exposed some of the porphyries to relatively recent denudation and consequently made them available for economic exploitation.

Composition and origin of ore-forming fluids in a carbonate-hosted porphyry copper and skarn deposit; a fluid inclusion and stable isotope study of Mines Gaspe, Quebec

Skarn-type ore bodies formed at temperatures near 350 degrees C. Salinities suggest progressive dilution of an early high salinity magmatic fluid by less saline meteoric water. Salinities of the porphyry copper ore fluids reflect two distinct fluids of high and moderate salinity. Three distinct thermal fluids are associated with late-stage porphyry copper ore deposition. Maximum temperature isotherms. Localization of the largest ore concentrations was the result of rapid cooling of the ore-bearing fluids by convecting meteoric waters. For the skarn-type ore bodies, fluid flow was stratigraphically controlled within preferred stratigraphic units.--Modified journal abstract.

Papua New Guinea´s Foreign Policy: A Bridge to Indonesian Shores

On 4 February 1982, after protracted negotiations, Papua New Guinea (PNG) and Indonesia signed agreements regulating the navigation of the Fly River which at its bulge west of 141? East Longitude is the border between PNG and Indonesia's Irian Jaya province (West New Guinea). The importance of this agreement to PNG cannot be overestimated for it is an integral requirement in the planned development of the Ok Tedi mine and other potential mineral resources in PNG's wild and remote Western Province. The Ok Tedi project is located at Mt. Fubilan in the Star mountain range some 18 kilometres east of the PNG-Indonesian border. The final agreement to develop the Ok Tedi mine was reached in February 1981, by a consortium consisting of Australia's BHP (Broken Hill Proprietary Co. Ltd., 30 per cent) and Amoco (30 per cent), the West German combine Kupferrexploration (20 per cent), and the PNG Government (20 per cent). It is hoped that the open-cut mine will be in production by 1985. Its low-grade gold cap is expected to pay for the infrastructure. The medium grade porphyry copper ore will be concentrated, filtered, and dried on site and then transported by barge 1,300 kilometres down the Fly River to Port Moresby for export. Hence, the necessity for an agreement with Indonesia for navigation on that part of the river where the thalweg forms the boundary.1 The promise of Ok Tedi comes at a critical time for PNG. The economy is heavily dependent on the 4Cs ? copper, cocoa, copra, and coffee. As the Bougainville mine goes deeper, its ore grade is declining. At the same time the North Solomon Province continues to insist on a larger share of the mine's income. Declining world prices for the 4Cs has already led to a significant drop in export earnings, forcing severe cutbacks in government expenditures across the full range of functions: from education and health to defence. More extensive exploitation of PNG's mineral resources, therefore, has

Fluid inclusions in calcite of some ore deposits in Roumania

Calcites from hydrothermal, porphyry copper and skarn ore deposits from Roumania contain two-phase fluid inclusions (liquid + vapour) with a vapour phase of 2–90% of the inclusion volume. Calcite from pyroxene hornfels, associated with phlogopite, pyrrotite, diopside and other minerals, contains inclusions with aqueous solution + vapour + halite. Homogenization temperatures of fluid inclusions in calcites from the first three groups of ore deposits, lie in the range from 60° to 480°C and the salinities vary from 5 to 23 wt.% NaCl. In calcite from pyroxene hornfels, the homogenization temperatures vary from 290° to 340°C and salinities range from 30 to 33 wt.% NaCl. The relationship between the crystal habit of calcite and the homogenization temperature shows the possibility of using fluid inclusions in the study of crystallogenesis.