Effect of salinity on osmoregulation and survival of a rhizocephalan parasite,Loxothylacus panopaei,and its crab host,Rhithropanopeus harrisii

The rhizocephalanLoxothylacus panopaei parasitizes the estuarine crabRhithropanopeus harrisii. Parasitized crabs are abundant during summers when salinities increase to around 15‰ in the crab–s habitat and scarce when salinities are lower. The two hypotheses that were proposed to explain this pattern were (1) that the parasite interferes with crab osmoregulation causing the host to die in low salinity water and (2) that salinity tolerance of the parasite larvae controls the incidence of parasitism. The first hypothesis was shown to be incorrect because (1) osmoregulation of infected crabs was, not altered by the parasite and (2) crab mortality did not increase in low salinity water down to 1‰. Unparasitized and parasitized crabs and the parasite itself were hypersomotic at low salinities (below 27‰ for the crabs). The parasite became slightly hyperosmotic at high salinities while the crabs were slightly hypoosmotic. The second hypothesis appears correct, becauseL. panopaei larvae survived poorly in salinities below 10‰ but well in salinities from 10 to 15‰. ThusR. harrisii, have a reproductive refuge at salinities below 10‰, because parasite larvae cannot survive and infect the mud crab at these low salinities.     

Salinity preferences in the stage I zoeae of three temperate zone fiddler crabs,genus Uca

Zoeae of three species of temperate zone fiddler crabs, Uca pugnax, U. minax, and U. pugilator, were reared in the laboratory. The zoeae of each species were placed individually in artificial salinity gradients and observed for specific salinity preferences. Each species of zoeae displayed a salinity preference that reflected the salinity patterns of the adult crabs of the same species. Zoeae of U. pugnax and U. pugilator, like the adult crabs, displayed a preference for higher salinities (i.e., 20.6‰±3.5 and 21.5‰±3.0, respectively). Zoeae of U. minax, like the adult crabs, displayed a preference for lower salinities (i.e., 9.8‰±2.9).     

Effect of salinity and temperature on survival and development of young zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels

We reared larval zebra mussels,Dreissena polymorpha, and quagga mussels,D. bugensis, through and beyond metamorphosis (settlement) at salinities of 0–8‰. Juvenile zebra mussels gradually acclimated to 8‰ and 10‰ have been reared at these salinities for over 8 mo. Tolerance to both higher temperatures and higher salinities increases with larval age in both species (though zebra mussel embryos and larvae have a greater degree of salinity tolerance than quagga mussel embryos and larvae). Thus, only 6% of 3-day-old zebra mussel veligers survived after exposure to 4‰ for 8 additional days, whereas there was 22% survival of veligers placed in 4‰ at day 13 and grown to settlement 11 d later. Zebra mussel pediveligers, acclimated to increasing salinity in 2‰ increments beginning at day 23, continued to survive and grow in 8‰ after 5-mo exposure, though the growth rates of these juveniles were significantly less than those of juveniles reared in lower salinities. Quagga mussels did not metamorphose and settle as quickly as zebra mussel pediveligers. No quagga mussel pediveligers had settled before exposure to artificial fresh water (AFW), 2‰ 4‰, 6‰, and 8‰ on day 30. Percent settlement of these quagga mussel juveniles (based on 100% survival at the start of experiments on day 30) was 90% in AFW, 67% at 2‰, 69% at 4‰, 46% at 6‰, and 0.1% at 8‰.     

Growth and mortality rates of larval American shad,Alosa sapidissima,at different salinities

The tolerance of post yolk-sac American shad Alosa sapidissima larvae to salinities typically seen in estuaries was assessed experimentally. Sixteen-day-old Hudson River (experiment I) and 35-d-old Delaware River (experiment II) larvae were held for 8 d and 9 d respectively in low (0–1‰), medium (9–11‰), and highly (19–20‰) brackish water, and mortality and growth rates were measured. Growth rates did not vary significantly among salinity treatments. Mortality in experiment I did not vary significantly among salinity treatments however, in experiment II, mortality was zero at 10‰ but higher and statistically indistinguishable between 0‰ and 20‰ In experiment II relative condition increased with salinity. These results imply that estuarine salinities neither depress growth rates nor elevate mortality rates of larval American shad when compared with freshwater conditions. We conclude that ecological factors other than the physiological effects of salinity have played more important roles in the evolution of the upriver spawning and nursery preference shown by this species.     

Larval production of the caridean shrimp,Crangon septemspinosa,in waters adjacent to Chesapeake Bay in relation to oceanographic conditions

Plankton samples of the MECCAS- (Microbial Exchanges and Coupling in Coastal Atlantic Systems) Project, taken in February, June, and August 1985 and April 1986, were analyzed to study the spatio-temporal distribution of sand shrimp, Crangon septemspinosa, larvae of Chesapeake Bay. With up to 250.9 larvae m^?3, results confirm C. septemspinosa as a very abundant decapod larval form in early spring in the study area. The overwhelming majority (94.5%) of the larvae occurred in April 1986; a second minor peak of larval production was observed in February 1985. The first two larval stages comprised 81.1% of the collected larvae, and complete series of all developmental stages including juveniles were obtained in June 1985 and April 1986. Newly hatched larvae occurred over a wide range of salinities (22.00–33.60‰), while more advanced forms were found mainly at higher salinities (>30‰). High larval abundances (>50 larvae m^?3) were obtained between 10°C; another considerably smaller peak in abundance occurred at temperatures ranging from 2.7°C to 4.5°C. Compared to other developmental stages, high abundances of the first two larval stages were collected at the highest chlorophyll concentrations. The significance of phytoplankton as a possible energy source for early stages of planktonic larvae and the role of phytoplankton as a possible chemical stimulus for larval release is discussed in terms of stomach and mouthpart structure and larval sensitivity to their chemical environment. *** DIRECT SUPPORT *** A01BY066 00016     

Influence of salinity on atrazine toxicity to a Chesapeake Bay copepod (Eurytemora affinis) and fish (Cyprinodon variegatus)

The objective of this study was to determine the influence of a range of salinities (5%., 15%., and 25%.) on the acute toxicity of atrazine to nauplii of the copepodEurytemora affinis and larvae of the sheepshead minnow,Cyprinodon variegatus. Ninety-six-hour LC50 values for the copepod were 0.5 mg 1^?1, 2.6 mg 1^?1, and 13.2 mg 1^?1 at salimities of 5%., 15%. and 25%. respectively. A comparison of LC50 values between adjacent salinities showed a statistical difference between 15%. and 25%. but not between 5%. and 15%.. Atrazine was more toxic toE. affinis at the lowest salinity. The 96-h LC50s for the sheepshead minnow were 16.2 mg 1^?1, 2.3 mg 1^?1, and 2.0 mg 1^?1 at salinities of 5%., 15%., and 25%., respectively. There was a statistical difference between LC50 values at 5%. and 15%. but not between 15%. and 25%.. In contrast toE. affinis results, atrazine was more toxic toC. variegatus at the highest salinity. The toxicity data from these species suggest that development of estuarine water quality criteria is warranted.     

Salinity tolerance of brown shrimpFarfantepenaeus aztecus as it relates to postlarval and juvenile survival, distribution, and growth in estuaries

The brown shrimp,Farfantepenaeus aztecus, is the major component of the Gulf of Mexico shrimp fishery, and it is critical that we understand its environmental requirements. Brown shrimp spend a large portion of their post-larval (PL) and juvenile life within estuaries distributed along salinity gradients and yet our understanding of the salinity tolerance of various age groups is limited. A series of 48-hr bioassays were conducted in which various ages ofF. aztecus (PL-10, PL-13, PL-15, PL-17, PL-20, and PL-23) were acclimated from a salinity of 26‰ to 1‰, 2‰, 4‰, 8‰, 12‰, and 26‰ in order to determine their tolerance to these salinities. Finally, PL-80.F. aztecus were transferred directly from 25‰ to 2‰, 4‰, and 8‰ waters to study the effects of rapid salinity reductions on juvenile survival. Survival of 10-and 13-day-old PLs was significantly, different from the control (26‰) for all salinities tested. Survival of PL-15 shrimp and older was significantly lower than survival of the controls at 1‰ and 2‰ but similar to the control at all other salinities tested. A 4-wk growth trial was conducted with juvenile shrimp at 2‰, 4‰, 8‰, and 12‰. There was no significant difference in survival among treatments, although shrimp maintained at 8‰ and 12‰ grew significantlymore than shrimp maintained at 2‰ and 4‰. There was no growth difference between shrimp at the two low salinities or between shrimp at the two high salinities. Survival of juveniles transferred directly from 25‰ to various salinities were 100% at 25‰, 94.2% at 8‰, 67.3% at 4‰, and 63.5% at 2‰. These results suggest that PL-13 and younger brown shrimp would have a better chance of survival by delaying entry into estuaries susceptible to rapid salinity declines. The brown shrimp juveniles would, be more densely distributed in areas with salinities greater than 4‰ than in salinities less than 4‰. Although food availability, and bottom type also affect shrimp distribution survival and growth, salinity may also greatly affect the shrimp and its fishery.     

Distribution and abundance of grapsid crabs (Grapsidae) in a mangrove estuary: Effects of sediment characteristics,salinity tolerances,and osmoregulatory ability

Crabs (Grapsidae,Sesarma) are the dominant macrofaunal group of mangrove forest soils in northern Australia. Little is known about the ecology of these crabs or the factors that influence their distribution in mangrove forests. Pitfall traps were used to sample grapsid crabs in the Murray River estuary in north Queensland. Sampling was conducted at five sites along a salinity gradient from <1‰ at upstream sites to >35‰ at the river mouth. At each site, trapping was done in both low and high intertidal forests. We characterized the sediments at each site by measuring percent sand, silt, clay and organic matter, Eh, pH, and soil pore-water salinity. Four species of grapsids dominated the crab fauna along the Murray River (Sesarma semperi-longicristatum, S. messa, S. brevicristatum, andS. brevipes). Distinct zonation patterns were found along the salinity gradient and between high and low intertidal forests.S. messa was dominant in high intertidal, downstream forests, high and low intertidal forests in the middle to downstream portion of the river, and in low intertidal forests in the central reach of the river.S. brevipes was dominant in both low and high intertidal zone forests at low salinity upstream sites.S. brevicristatum was most abundant in the central reaches of the river and only in the high intertidal zone.S. semperi-longicristatum was found only in the low intertidal zone, downstream forest. Subsequently, tests of salinity tolerances of these crabs were carried out in the laboratory. These indicated very wide tolerances over salinities from completely fresh to hypersaline (60‰). The osmoregulatory abilities of the crabs were also found to vary. However, neither their salinity tolerance nor osmoregulatory ability adequately explain the zonation patterns were measured in the field. For example,S. brevicristatum had the most restricted distribution, but it had the second broadest salinity tolerance and osmoregulatory ability. Sediment characteristics explained a significant amount of the variation in abundance for two of the crab species. Pore-water salinity provided no explanatory power for any of the species. Individual species abundances are probably influenced by additional factors such as interspecific competition and predation.     

Salinity detection and associated behavior in the dungeness crab,Cancer magister

Dungeness crabs, Cancer magister, showed the same antennular flicking response to brief (<2 min) salinity fluctuations as they have previously shown in detecting chemical food cues during other studies. The threshold concentrations at which 50% of the crabs detected the salinity changes were 29.9‰ and 32.7‰ or 96% and 105% of ambient seawater (31.0‰). At the maximum salinity changes used, other behaviors accompanied the flicking response. In a second experiment where salinity rose or fell continuously, two previously undescribed behaviors, pulsing and closure, occurred. In pulsing, crabs showed a rapid coordinated opening and closing of the outer maxillipeds with rapid beating of the maxillipedal flagellae. In closure, crabs stopped all overt activity, retracted their appendages and tightly closed the buccal cavity with the outer maxillipeds. Under increasing salinity crabs exhibited pulsing at 34.9‰ or 113% of ambient seawater and closure at 36.2‰ or 117% of ambient. Under decreasing salinity crabs showed pulsing at 23.2‰ or 75% of ambient seawater and closure at 15.5‰ or 50% of ambient.     

Subtidal distribution of barnacles (Cirripedia: Balanidae) in Chesapeake Bay,Maryland

From 1977 to 1980, samples of barnacles were collected (as opportunities arose) from 61 subtidal locations (mostly oyster beds) around Chesapeake Bay, Maryland. Three species were identified from the area.Balanus improvisus dominated, comprising 83% of the 8,231 barnacles identified, and was collected at all locations but one. It occurred over a collection salinity range of 0.8‰ to 17.9‰.Balanus subalbidus (14% of the barnacles identified) was collected over the same salinity range, but mainly in lower salinity waters.Balanus eburneus was scarce (2% of the barnacles identified) and was collected at higher salinities (8.5‰ to 17.1‰).     

Mechanisms of expansion for an introduced species of cordgrass, Spartina densiflora, in Humboldt Bay, California

The dominant plant in Humboldt Bay salt marshes in Spartina densiflora, a species of cordgrass apparently introduced from South America. At several salt marshes and restoration sites around Humboldt Bay, distribution of this plant has increased significantly. We investigated the relative contributions of vegetative tiller production and seed germination to the establishment and expansion of S. densiflora. Lateral spread of plants surrounded by competitors were compared to areas without competing plant species. Plants growing in areas without competitors had significantly higher rates of vegetative expansion (p<0.0001). Viable seed production, germination rates, seedling survivorship, and growth of adult plants were measured in six salinity treatments. Approximately 1,977±80 viable seeds are produced per plant (0.25–0.5 m²). The number of germinating seeds was inversely related to increases in salinity. Salinity treatments between 19‰ and 35‰ produced significantly lower germination rates than salinities of 0–18‰ (p<0.0001). Seedling survivorship was 50% at ≤4‰ and 8–14% at ≥11‰. Lateral expansion of adult, greenhouse-grown plants occurred in all salinity treatments, with modest decreases in the highest salinity treatments (p<0.05). Our findings indicate that S. densiflora expands primarily by vegetative expansion, and lateral tillers are produced by throughout the year. Spartina densiflora produces prolific amounts of seed, but recruitment in mature salt marshes may be limited by competitors and higher salinities. At restoration sites, planting of native species such as Salicornia virginica, Distichlis spicata, or Jaumea carnosa may prevent monospecific stands of S. densiflora from developing.     

Using submerged aquatic vegetation to establish minimum and maximum freshwater inflows to the Caloosahatchee estuary, Florida

Species of submerged aquatic vegetation (SAV) are frequently used in the management of estuarine systems to set restoration goals, nutrient load reduction goals, and water quality targets. As human need for water increases, the amount of freshwater required by estuaries has become an increasingly important issue. While the, science of establishing the freshwater needs of estuaries is not well developed, recent attempts have emphasized the freshwater requirements of fisheries. We evaluate the hypothesis that SAV can be used to establish freshwater inflow needs. Salinity tolerance data from laboratory and field studies of SAV in the Caloosahatchee estuary, Florida, are used to estimate a minimum flow required to maintain the salt-tolerant freshwater species,Vallisneria americana, at the head of the estuary and a maximum flow required to prevent mortality, of the marine speciesHalodule wrightii at its mouth. ForV. americana, laboratory experiments showed that little or no growth occurred between 10‰ and 15‰ In the field, lower shoot densities (<400 shoots m^?2) were associated with salinities greater than 10‰. Results forH. wrightii were more variable than forV. americana. Laboratory experiments indicated that mortality could occur at salinities <6‰, with little growth occurring between 6‰ and 12‰. Field data indicated that higher blade densities (>600 blades m^?2) tend to occur at salinities greater than 12‰ Relationships between salinity in the estuary and discharge from the Caloosahatchee River indicated that flows>8.5 m³ s^?1 would produce tolerable salinity (<10‰) forV. americana and flows<89 m³ s^?1 would avoid lethal salinities (<6‰) forH. wrightii.     

Prey density requirements of the striped bass,Morone saxatilis (Walbaum), larvae

Striped bass,Morone saxatilis, larvae of 9 DAH (days after hatching) were fed for 16 d with five densities of adults (5–100 l^?1), copepodites (10–200 l^?1), and nauplii (50–1,000^?1) of the copepodEurytemora affinis, and 5-DAH and 10-DAH larvae were fed at seven densities (5–500 l^?1) of brine shrimp,Artemia salina, nauplii. The study determined the effects of prey types and densities on the survival and growth of the fish larvae, and the effects of delaying first feeding from 5 DAH to 10 DAH. The survival and grwoth of the larvae fedE. affinis adults was higher than those fedE. affinis copepodites.E. affinis nauplii were the poorest prey. OneE. affinis adult provided nutrition equivalent to 1.45 copepoditer or 11.12 nauplii. The percentage survival of the larvae was higher for those fedA. salina nauplii thanE. affinis adults at the densities below 67.25 l^?1, but there was no difference at this density or higher. Delaying first feeding from 5 DAH to 10 DAH did not affect percentage survival and size of larvae at the end of the experiments. Because the survival and growth of the larvae increased as the prey density increased, it was difficult to set a point along the regression line as the minimum density requirement level. It may be said that for striped bass larvae, the higher the prey density, the higher the survival and growth, and thus the greater the recruitment success.     

Seasonal abundance of atlantic croaker (Micropogonias undulatus) in relation to bottom salinity and temperature in South Carolina estuaries

During 1973 and 1974 seasonal abundance and mean total length of Atlantic croaker,Micropogonias undulatus, were investigated by otter trawl at 33 stations in South Carolina estuaries in relation to bottom salinity and temperature. Relative abundance of Atlantic croaker was measured by catch per unit effort at 3°C temperature intervals and 3‰ salinity intervals. Croaker occurred over a bottom temperature range of 9.0–31.4°C while occurring most abundantly in waters above 24.0°C. No significant correlation between size and temperature was found. Croaker were collected in salinities from 0.4 to 34.4‰. High correlations of size and salinity were evident in 1973 during winter (r=0.79), summer (r=0.82), and fall (r=0.94). In 1974, correlations were significant only during fall (r=0.76).     

Swimming speeds of oyster larvaeCrassostrea virginica in different salinities and temperatures

Swimming speeds of oyster larvaeCrassostrea virginica were determined in constant and increasing salinities to learn more about the oyster larval “salinity response”. “Normal” non-directed swimming speeds ranged from less than 1 cm/min for early veligers to 5 cm/min for “eyed” veligers with temperature an important variable. When subjected to hourly salinity increases of 0.5‰, most larvae swam upward or downward at approximately 3 times the above speeds. Larvae with values closed in response to traces of formalin sank at speeds of 5 to 50 cm/min depending on larval stage. The results may explain the differential vertical position of larval stages in estuaries and suggest the presence of a taxic component to the salinity response.     

The growth of submersed macrophytes under experimental salinity and light conditions

The growth, morphology, and chemical composition ofHydrilla verticillata, Myriophyllum spicatum, Potamogeton perfoliatus, andVallisneria americana were compared among different salinity and light conditions. Plants were grown in microcosms (1.2 m⁵) under ambient photoperiod adjusted to 50% and 8% of solar radiation. The culture solution in five pairs of tanks was gradually adjusted to salinities of 0, 2, 4, 6, and 12‰. With the exception ofH. verticillata, the aquatic macrophytes examined may be considered eurysaline species that are able to adapt to salinities one-third the strength of sea water. With increasing salinity, the inflorescence production decreased inM. spicatum andP. perfoliatus, yet asexual reproduction in the latter species by underground buds remained constant. Stem elongation increased in response to shading inM. spicatum, while shadedP. perfoliatus had higher concentrations of chlorophylla. In association with high epiphytic mass, chlorophylla concentrations in all species were greatest at 12‰. The concentration of sodium increased in all four species of aquatic macrophytes examined here, indicating that these macrophytes did not possess mechanisms to exclude this ion. The nitrogen content (Y) of the aquatic macrophytes tested increased significantly with higher sodium concentration (X), suggesting that nitrogen may be utilized in osmoregulation (Y = X × 0.288 + 6.10, r² = 0.71). The tolerance ofV. americana andP. perfoliatus to salinity was greater in our study compared to other investigations. This may be associated with experimental methodology, whereby macrophytes were subjected to more gradual rather than abrupt changes in salinity. The two macrophytes best adapted to estuarine conditions in this study by exhibiting growth up to 12‰, includingM. spicatum andV. americana, also exhibited a greater degree of response in morphology, tissue chemistry (including chlorophyll content and total nitrogen), and reproductive output in response to varying salinity and light conditions.     

Dynamics of pink shrimp (Farfantepenaeus duorarum) recruitment potential in relation to salinity and temperature in Florida Bay

Progress is reported in relating upstream water management and freshwater flow to Florida Bay to a valuable commercial fishery for pink shrimp (Farfantepenaeus duorarum), which has major nursery grounds in Florida Bay. Changes in freshwater inflow are expected to affect salinity patterns in the bay, so the effect of salinity and temperature on the growth, survival, and subsequent recruitment and harvest of this ecologically and economically important species was examined with laboratory experiments and a simulation model. Experiments were conducted to determine the response of juvenile growth and survival to temperature (15°C to 33°C) and salinity (2‰ to 55‰), and results were used to refine an existing model. Results of these experiments indicated that juvenile pink shrimp have a broad salinity tolerance range at their optimal temperature, but the salinity tolerance range narrows with distance from the optimal temperature range, 20–30°C. Acclimation improved survival at extreme high salinity (55‰), but not at extremely low salinity (i.e., 5‰, 10‰). Growth rate increases with temperature until tolerance is exceeded beyond about 35°C. Growth is optimal in the mid-range of salinity (30‰) and decreases as salinity increases or decreases. Potential recruitment and harvests from regions of Florida bay were simulated based on local observed daily temperature and salinity. The simulations predict that potential harvests might differ among years, seasons, and regions of the bay solely on the basis of observed temperature and salinity. Regional differences in other characteristics, such as seagrass cover and tidal transport, may magnify regional differences in potential harvests. The model predicts higher catch rates in the September–December fishery, originating from the April and July settlement cohorts, than in the January–June fishery, originating from the October and January settlement cohorts. The observed density of juveniles in western Florida Bay during the same years simulated by the model was greater in the fall than the spring, supporting modeling results. The observed catch rate in the fishery, a rough index of abundance, was higher in the January–June fishery than the July–December fishery in most of the biological years from 1989–1990 through 1997–1998, contrary to modeling results and observed juvenile density in western Florida Bay.     

Recruitment of the Crabs Eurypanopeus depressus, Rhithropanopeus harrisii, and Petrolisthes armatus to Oyster Reefs: the Influence of Freshwater Inflow

Oyster reefs provide structural habitat for resident crabs and fishes, most of which have planktonic larvae that are dependent upon transport/retention processes for successful settlement. High rates of freshwater inflow have the potential to disrupt these processes, creating spatial gaps between larval distribution and settlement habitat. To investigate whether inflow can impact subsequent recruitment to oyster reefs, densities of crab larvae and post-settlement juveniles and adults were compared in Estero Bay, Florida, over 22 months (2005–2006). Three species were selected for comparison: Petrolisthes armatus, Eurypanopeus depressus, and Rhithropanopeus harrisii. All are important members of oyster reef communities in Southwest Florida; all exhibit protracted spawning, with larvae present throughout the year; and each is distributed unevenly on reefs in different salinity regimes. Recruitment to oyster reefs was positively correlated with bay-wide larval supply at all five reefs examined. Species-specific larval connectivity to settlement sites was altered by inflow: where connectivity was enhanced by increased inflow, stock–recruitment curves were linear; where connectivity was reduced by high inflows, stock–recruitment curves were asymptotic at higher larval densities. Maximum recruit density varied by an order of magnitude among reefs. Although live oyster density was a good indicator of habitat quality in regard to crab density, it did not account for the high variability in recruit densities. Variation in recruit density at higher levels of larval supply may primarily be caused by inflow-induced variation in larval connectivity, creating an abiotic simulation of what has widely been regarded as density dependence in stock–recruitment curves.     

Micrometallogeny and hydrothermal fluid evolution of the Iju porphyry Cu deposit,NW Kerman,Iran: Evidence from fluid inclusions,Laser Raman spectroscopy,and SO isotope systematics

The Iju Cu porphyry is located in the NW part of the Kerman Magmatic Copper Belt (KMCB). It is related to a ~ 9 Ma granodiorite porphyry intrusion, with three main stages of hydrothermal activity. The homogenization temperatures for the fluid inclusions are in the ranges of 200–494 °C, and their salinities vary from 4.0 to 42.8 wt% NaCl equiv., which are typical magmatic-hydrothermal fluids. The δ³⁴S values of sulfides range from −0.4 to +3.2 ‰ (V-CDT), and the δ³⁴S values of anhydrite samples range from +11.6 to +16.8 ‰. The δ³⁴S values of sulfides show a narrow range, implying a homogeneous sulfur source. The oxygen isotopic composition of hydrothermal water in equilibrium with quartz samples ranges from +3.4 to +6.0 ‰ (V-SMOW) consistent with the hydrothermal fluids having a magmatic signature, but diluted with meteoric waters in the main mineralizing stage. The most important factors responsible for metal precipitation in the Iju porphyry deposit are fluid boiling, oxygen fugacity decrease and cooling followed by dilution with meteoric water. The primary fluids of the Iju Cu deposit are characterized by relatively high temperature and moderate salinity, and are CO₂-rich, indicating a typical post-collisional porphyry system.     

西藏恰功矽卡岩铁矿床成矿流体特征及演化:对Fe-Pb矿化的约束

目前关于恰功矽卡岩型铁矿床的流体演化过程及成矿机制,尤其是铁-铅矿体的成矿作用尚缺研究.对不同阶段的主要矿物进行包裹体均一温度-盐度、激光拉曼光谱分析以及H-O同位素测试.进矽卡岩阶段包裹体均一温度为400~550℃;盐度为15.5%~20.9% NaCl_eqv,其中S型盐度高达56.5% NaCl_eqv;气液相成分均为H₂O.退化蚀变阶段包裹体均一温度为350~420℃;盐度集中于14.1%~16.6% NaCl_eqv,少量为2%~8% NaCl_eqv,而S型包裹体盐度亦高达55.8% NaCl_eqv;气液相成分均为H₂O,液相富含HCO₃-和CO₃2-.石英-方铅矿阶段包裹体均一温度范围为238~343℃,对应盐度为3.1~13.9% NaCl_eqv,其中含CO₂三相包裹体完全均一温度集中在290~310℃,盐度为1.6%~11.2% NaCl_eqv.石英-方解石阶段包裹体均一温度与盐度分别为242~360℃和1.7%~11.8% NaCl_eqv,气液相成分均为H₂O.H-O同位素显示:进矽卡岩阶段δD_H2O为-106.4‰~-113.2‰,δ18O_H2O为6.2‰~8.0‰;退化蚀变阶段δD_H2O为-84.8‰~-130.1‰,δ18O_H2O为2.7‰~5.5‰,退化蚀变阶段δ18O_H2O值相对进矽卡岩阶段低;石英-方铅矿阶段δD_H2O为-95.3‰~-103.8‰,δ18O_H2O为-1.6‰~-0.7‰;石英-方解石阶段δD_H2O为-67.4‰~-101.0‰,δ18O_H2O为-0.8‰~0.6‰.结果表明流体整体具有从高温、中-高盐度逐渐向低温、低盐度演化的特征,矽卡岩期成矿流体来源于岩浆出溶;矽卡岩期流体的不混溶作用并与围岩发生反应是磁铁矿沉淀的重要机制,石英-方铅矿阶段流体温压下降是方铅矿沉淀的根本原因.