The study of fluid inclusions is important for understanding various geologic processes involving geofluids. However, there are a number of problems that are frequently encountered in the study of fluid inclusions, especially by beginners, and many of these problems are critical for the validity of the fluid inclusion data and their interpretations. This paper discusses some of the most common problems and/or pitfalls, including those related to fluid inclusion petrography, metastability, fluid phase relationships, fluid temperature and pressure calculation and interpretation, bulk fluid inclusion analysis, and data presentation. A total of 16 problems, many of which have been discussed in the literature, are described and analyzed systematically. The causes of the problems, their potential impact on data quality and interpretation, as well as possible remediation or alleviation, are discussed.

The Proterozoic Athabasca Basin is well known for its unusually large-tonnage and high-grade ‘unconformity-related’ uranium (U) deposits, however, explanations for the basin-wide U endowment have not been clearly identified. Previous studies indicate that U-rich brines with up to ~600 ppm U and variable Na/Ca ratios (from Na-dominated to Ca-dominated) were present at the sites of U mineralization, but it is unknown whether such fluids were developed solely in the vicinity of the U deposits or at a basinal scale. Our microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz overgrowths from the barren part of the basin indicate that U-rich brines (0.6 to 26.8 ppm U), including Na-dominated and Ca-dominated varieties, were widely developed in the basin. These U concentrations, although not as high as the highest found in the U deposits, are more than two orders of magnitude higher than most naturally occurring geologic fluids. The basin-scale development of U-rich diagenetic fluids is interpreted to be related to several geologic factors, including availability of basinal brines and U-rich lithologies, and a hydrogeologic framework that facilitated fluid circulation and U leaching. The combination of these favorable conditions is responsible for the U fertility of the Athabasca Basin.

A porphyritic granite intrusion was recently discovered in the Zhuanzhilian section of the Dongping gold deposit. There is as many as one tonnage of Au in the fractured shear zone within the porphyritic granite intrusion, but no relevant reports concerning the origin and age of the intrusion has been published as yet. In this paper, zircon U-Pb dating is used to study the geochronology of porphyritic granite, in order to find out the evidence of age and the relationship with gold mineralization. There are two groups of zircon 207Pb/235U-206Pb/238U concordant ages of porphyritic granites: The concordant age of 373.0 ± 3.5 Ma, with the weighted mean age of 373.0 ± 6.4 Ma; and the concordant age of 142.02 ± 1.2 Ma with the weighted mean age of 142.06 ± 0.84 Ma. We believe that the first group might represent the age of residual zircon of alkaline complex, while the second group might be related with main gold mineralization. The obtained results of the petrography and electron probe analysis indicate that the porphyritic quartz and porphyritic granite, as well as gold mineralization, might be products of a late replacement of tectonic-hydrothermal fluid, which was rich in Si, Na and K originally and later yielded gold-forming fluids.

The Proterozoic Athabasca Basin hosts a large number of high-grade, large-tonnage unconformity-related uranium (U) deposits, many of which are also enriched in rare earth elements (REE). The basin also contains hydrothermal REE mineralization unassociated with U. Previous studies postulated that U and REE were derived from either the basin or the basement; however, the exact source of the metals remains ambiguous. This study provides evidence of U- and REE-rich fluids throughout the Athabasca Basin through laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) mapping of barren sandstone distal to mineralized areas. The results indicate that elevated U and REE concentrations mainly occur in the matrix; there are strong positive correlations between U and REE, Th, P and Sr, and moderate positive correlations between U and Zr, Ba, Fe, Al, K and Ca, but the few spots with the highest U are unrelated to these elements. Quantitative evaluation of the element correlations, together with scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis, suggests that most of the elevated U and REE are hosted in aluminum phosphate sulfate (APS) minerals rather than apatite and monazite. As the APS minerals are of diagenetic-hydrothermal origin, the results testify to the presence of U- and REE-rich fluids within the Athabasca Basin. The elevated Th/U ratio (~10) and REE pattern (strong heavy rare earth element (HREE) depletion) are consistent with a model in which large amounts of U and REE (especially HREE) were leached from the sandstone within the Athabasca Basin and contributed to U and REE mineralization near the unconformity between the sedimentary rocks in the basin and underlying basement rocks. This study demonstrates that LA-ICP-MS mapping can be effectively used to evaluate microscale distribution of elements and their mobility in sedimentary rocks to address mineralization related problems.

The temporal–spatial relationships of porphyry and orogenic gold mineralization in the Eastern Tianshan Orogenic Belt are ambiguous. The newly discovered Changshagou deposit in this belt contains both porphyry and orogenic gold mineralization, which are characterized by polymetallic–sulfide veinlets and quartz–pyrite veins, respectively. Fluid inclusions in the porphyry mineralization episode were trapped at 290–340°C with salinities of 3.0–8.0 wt% NaCl _equiv . The homogenization temperatures and salinities in the orogenic mineralization episode range from 240 to 300°C and from 1.0 to 5.0 wt% NaCl _equiv . Coexisting V- and L-type fluid inclusions with similar homogenization temperatures are indicative of fluid immiscibility. The δ ¹⁸ O _w and δ D _w values are in the ranges 7.6–9.1 and −70.9 to −84.0‰ in the porphyry mineralization episode, and 6.4–7.1 and −65.7 to −72.1‰ in the orogenic mineralization episode, overlapping magmatic and metamorphic ranges, respectively. The pyrite δ ³⁴ S values range from 3.5 to 4.9‰, falling into the magmatic range. Pyrite in porphyry and orogenic mineralization episodes yield Re–Os isotope ages of 269.1 ± 2.9 and 257.4 ± 2.4 Ma. The porphyry and orogenic gold mineralizations are genetically associated with the quartz syenite porphyry and Kanggur strike-slip shear activity, respectively.