13 research outputs found
Transport of Pb and Zn by carboxylate complexes in basinal ore fluids and related petroleum-field brines at 100°C: the influence of pH and oxygen fugacity
It is well established through field observations, experiments, and chemical models that oxidation (redox) state and pH exert a strong influence on the speciation of dissolved components and the solubility of minerals in hydrothermal fluids. log [Image: see text] –pH diagrams were used to depict the influence of oxygen fugacity and pH on monocarboxylate- and dicarboxylate-transport of Pb and Zn in low-temperature (100°C) hydrothermal ore fluids that are related to diagenetic processes in deep sedimentary basins, and allow a first-order comparison of Pb and Zn transport among proposed model fluids for Mississippi Valley-type (MVT) and red-bed related base metal (RBRBM) deposits in terms of their approximate pH and [Image: see text] conditions. To construct these diagrams, total Pb and Zn concentrations and Pb and Zn speciation were calculated as a function of log [Image: see text] and pH for a composite ore-brine with concentrations of major elements, total sulfur, and total carbonate that approximate the composition of MVT and RBRBM model ore fluids and modern basinal brines. In addition to acetate and malonate complexation, complexes involving the ligands Cl(-), HS(-), H(2)S, and OH(- )were included in the model of calculated total metal concentration and metal speciation. Also, in the model, Zn and Pb are competing with the common-rock forming metals Ca, Mg, Na, Fe, and Al for the same ligands. Calculated total Pb concentration and calculated total Zn concentration are constrained by galena and sphalerite solubility, respectively. Isopleths, in log [Image: see text] –pH space, of the concentration of Pb and concentration of Zn in carboxylate (acetate + malonate) complexes illustrate that the oxidized model fluids of T. H. Giordano (in Organic Acids in Geological Processes, ed. E. D. Pittman and M. D. Lewan, Springer-Verlag, New York, 1994, pp. 319–354) and G. M. Anderson (Econ. Geol., 1975, 70, 937–942) are capable of transporting sufficient amounts of Pb (up to 10 ppm) and Zn (up to 100 ppm) in the form of carboxylate complexes to form economic deposits of these metals. On the other hand, the reduced ore fluid models of D. A. Sverjensky (Econ. Geol., 1984, 79, 23–37) and T. H. Giordano and H. L. Barnes (Econ. Geol., 1981, 76, 2200–2211) can at best transport amounts of Pb and Zn, as carboxylate complexes, that are many orders of magnitude below the 1 to 10 ppm minimum required to form economic deposits. Lead and zinc speciation (mol% of total Pb or Zn) in the model ore fluid was calculated at specific log [Image: see text] –pH conditions along the 100, 0.01, and 0.001 ppm total Pb and total Zn isopleths. Along the 100 ppm isopleth conditions are oxidized (∑SO(4 )>> ∑H(2)S) with Pb and Zn predominantly in the form of chloride complexes under acid to mildly alkaline conditions (pH from 3 to approximately 7.5), while hydroxide complexes dominate Pb and Zn speciation under more alkaline conditions. Sulfide complexes are insignificant under these oxidized conditions. For more reduced conditions along the 0.01 and 0.001 ppm isopleths chloride complexes dominate Pb and Zn speciation in the SO(4)(2- )field and near the SO(4)(2-)-reduced sulfur boundary from pH = 4 to approximately 7.5, while hydroxide complexes dominate Pb and Zn speciation under alkaline conditions above pH = 7.5 in the SO(4)(2- )field. In the most reduced fluids (∑H(2)S >> ∑SO(4)) along the 0.01 and 0.001 isopleths, sulfide complexes account for almost 100% of the Pb and Zn in the model fluid. Acetate (monocarboxylate) complexation is significant only under conditions of chloride and hydroxide complex dominance and its effect is maximized in the pH range 5 to 7, where it complexes 2 to 2.6% of the total Pb and 1 to 1.25% of the total Zn. Malonate (dicarboxylate) complexes are insignificant along all isopleths. The speciation results from this study show that deep formation waters characterized by temperatures near 100°C, high oxidation states and ∑H(2)S < 0.03 mg L(-1 )([Image: see text] < 10(-6)), high chlorinities (~ 100000 mg L(-1)), and high but reasonable concentrations of carboxylate anions can mobilize up to 3% of the total Pb and up to 1.3% of the total Zn as carboxylate complexes. Furthermore, these percentages, under the most favorable conditions, correspond to approximately 1 to 100 ppm of these metals in solution; concentrations that are adequate to form economic deposits of these metals. However, the field evidence suggests that all of these optimum conditions for carboxylate complexation are rarely met at the same time. A comparison of the composite ore fluid compositions from this study and modern brine data shows that the ore brines, corresponding to log [Image: see text] –pH conditions based on the Anderson (1975) and Giordano (1994) model fluids, are similar in many respects to modern, high trace-metal petroleum-field brines. The principal differences between modern high trace-metal brines and the composite ore fluids of Anderson (1975) and Giordano (1994) relate to their carboxylate anion content. The reported concentrations of monocarboxylate anions (∑monocbx) and dicarboxylate anions (Edicbx) in high trace-metal petroleum-field brines (< 1 to 300 mg L(-1 )and < 1 mg L(-1), respectively) are significantly lower than the concentrations assumed in the modelled brines of this study (∑monocbx = 7 700 mg L(-1 )and ∑dicbx = 300 mg L(-1)). There are also major differences in the corresponding total chloride to carboxylate ratio (∑m(Cl)/∑m(cbx)) and monocarboxylate to dicarboxylate ratio (∑m(monocbx)/∑m(dicbx)). Modern high trace-metal brines have much higher ∑m(Cl)/∑m(cbx )values and, therefore, the contribution of carboxylate complexes to the total Pb and Zn content in these modern brines is likely to be significantly less than the 1 to 3 percent for the composite ore fluids of Anderson (1975) and Giordano (1994). The composite ore-brine based on the Giordano and Barnes (1981) MVT ore fluid is comparable to the high salinity (> 170 000 mg L(-1 )TDS) subset of modern brines characterized by low trace-metal content and high total reduced sulfur (∑H(2)S). A comparison of the Sverjensky (1984) composite ore-brine with modern petroleum-field brines in terms of ∑H(2)S and Zn content, reveals that this ore fluid corresponds to a "border-type" brine, between modern high trace-metal brines and those with low trace-metal content and high ∑H(2)S. A brine of this type is characterized by values of ∑H(2)S, ∑Zn, and/or ∑Pb within or near the 1 to 10 mg L(-1 )range. Based on brine-composition data from numerous references cited in this paper, border-type brines do exist but are rare. The model results and field evidence presented in this study are consistent with other chemical simulation studies of carboxylate complexation in modern petroleum-field brines. Thus, it appears that carboxylate complexation plays a minor, if not insignificant, role as a transport mechanism for Pb and Zn in high salinity Na–Cl and Na–Ca–Cl basinal brines and related ore fluids
Reservoir quality of fluvial sandstone reservoirs in salt-walled mini-basins: an example from the Seagull field, Central Graben, North Sea, UK
Diagenesis and Hydrocarbon Accumulation, Brent Sandston (Jurassic), Bergen High Area, North Sea
Diagenetic paths in the margin of a Triassic Basin: NW zone of the Iberian Chain, Spain
Buntsandstein deposits generated in a slowly
subsiding basin on the western margin of the Iberian
Chain are represented by a stratigraphic succession of
fluvial deposits less than 100 m thick (conglomerates,
sandstones, and shales). Diagenetic processes in sandstones
can be grouped as eodiagenetic, mesodiagenetic,
and telodiagenetic. Eodiagenesis can be associated
with Muschelkalk, Keuper, and probably early Jurassic
times. Mesodiagenesis is probably related to
Jurassic times. Diagenetic chemical reactions suggest a
maximum burial less than 1.5 km and low temperatures
(<120ºC). Patterns of porosity reduction by
compaction and cementation suggest four diagenetic
stages: (1) Loss of primary porosity by early
mechanical compaction; (2) early cementation (Kfeldspar
and dolomite); (3) dissolution of cements; and
(4) framework collapse by re-compaction. These stages
are manifested by the presence of two types of sandstone.
Type I sandstones present high intergranular
volume (mean, 30%). Type II sandstones are characterized
by high compactional porosity loss and exhibit
low values of intergranular volume (mean, 16.9%).
Type II sandstones are associated with the dissolution
of cement and later re-compaction of type I sandstones.
An intermediate telodiagenetic phase is deduced
and related to the sharp unconformity between
Lower Cretaceous sediments and the underlying sediments.
This suggests that a mechanically unstable
framework collapsed during the Cretaceous, generating
type II sandstones. The analyzed diagenetic paths have
a wide applicability on similar marginal areas of rift
basins
Study on the effects of alcohol-enhanced air sparging remediation in a benzene-contaminated aquifer: a new insight
The radius of influence of a combined method of in situ air sparging and soil vapor extraction in the intertidal sediments of Gomso Bay on the west coast of South Korea
Characteristics and pore evolution of the tight sandstone reservoirs of the Chang-7 Member of the Yanchang Formation in the Xin’anbian area, Ordos basin
Mudrocks as Soft Rocks: Properties and Characteristics
Soft rocks comprise the geological materials with poor mechanical characteristics that span the range between soils and hard rocks. Mudrocks are part of the broader group of soft rocks which correspond to fine-grained, clay-rich detrital sedimentary rocks. As mudrocks constitute more than 60% of all sedimentary rocks and occur frequently in geological sequence, they are often encountered in construction sites either in their natural undisturbed state or as construction materials. Mudrocks can show a range of engineering behaviours as function of their composition and structural features; however, by reputation, they are regarded as poor engineering materials in construction displaying low strength and durability as well as susceptibility to volume changes. This chapter aims to provide a framework of the main geological and engineering geological aspects of mudrocks that control their engineering properties and behaviour. With this concern, the key controls on the formation of mudrocks, the terminology used to classify fine-grained sedimentary rocks and the main geological and geotechnical characteristics of mudrocks, including the relevant laboratory techniques are presented as well as the geological and engineering geological classifications of mudrocks are reviewed. Finally, a set of case studies of mudrocks encountered in commonly occurring civil engineering works are described