Minor and trace elements can substitute into the crystal lattice of galena at various concentrations. In situ LA-ICP-MS analysis and trace element mapping of a range of galena specimens from ...different deposit types are used to obtain minor/trace element data, aimed at achieving insight into factors that control minor/trace element partitioning. The previously recognized coupled substitution Ag++(Bi,Sb)3+ ⇌ 2Pb2+ is confirmed. However, the poorer correlation between Ag and (Bi+Sb) when the latter elements are present at high concentrations (∼>2000 ppm), suggests that site vacancies may come into play: 2(Bi,Sb)3++∎ ⇌ 3Pb2+. Galena is the primary host of Tl in all mapped mineral assemblages. Along with Cu, Tl is likely incorporated into galena via the coupled substitution: (Ag,Cu,Tl)++(Bi,Sb)3+ ⇌ 2Pb2+. Tin can reach significant concentrations in galena (>500 ppm). Cd and minor Hg can be incorporated into galena; the simple isovalent substitution (Cd,Hg)2+ ⇌ Pb2+ is inferred. This paper shows for the first time, oscillatory and sector compositional zoning of minor/trace elements (Ag, Sb, Bi, Se, Te, Tl) in galena from two epithermal ores. Zoning is attributed to slow crystal growth into open spaces within the vein at relatively low temperatures.The present data show that galena can host a broader range of elements than previously recognized. For many measured elements, the data sets generated display predictable partitioning patterns between galena and coexisting minerals, which may be dependent on temperature or other factors. Trace element concentrations in galena and their grain-scale distributions may also have potential in the identification of spatial and/or temporal trends within individual metallogenic belts, and as markers of ore formation processes in deposits that have undergone superimposed metamorphism and deformation. Galena trace element geochemistry may also display potential to be used as a trace/minor element vector approach in mineral exploration, notably for recognition of proximal-to-distal trends within a given ore system.
Laser ablation-inductively coupled plasma-mass spectrometry and electron-probe microanalysis were used to investigate the trace-element contents of sphalerite, chalcopyrite and pyrite from the Plaka ...Pb–Zn–Ag deposit. Using petrographic observations, the analytical results could be linked to the temporal evolution of the Plaka ore-forming system. Sphalerite chemistry reliably records the temperature and
f
S
2
evolution of the system, with estimated formation temperatures reproducing the microthermometric results from previous fluid-inclusion studies. Chalcopyrite chemistry also shows systematic variations over time, particularly for Cd, Co, Ge, In, Sn and Zn concentrations. Measurable pyrite was only found in association with early high-temperature mineralisation, and no clear trends could therefore be identified. We note, however, that As and Se contents in pyrite are consistent with formation temperatures estimated from co-existing sphalerite. Statistical analysis of the sphalerite data allowed us to identify the dominant geological controls on its trace-element content. The three investigated factors temperature,
f
S
2
, and sample location account for > 80% of the observed variance in Mn, Fe, Co, Ga, Ge, In, Sb and Hg concentrations, and > 60% of the observed variance in Cd and Sn concentrations. Only for Cu and Ag concentrations is the explained variance < 50%. A similarly detailed analysis was not possible for chalcopyrite and pyrite. Nevertheless, comparison of the results for all three investigated minerals indicates that there are some systematic variations across the deposit which may be explained by local differences in fluid composition.
Suspended microfluidics Casavant, Benjamin P.; Berthier, Erwin; Theberge, Ashleigh B. ...
Proceedings of the National Academy of Sciences,
06/2013, Letnik:
110, Številka:
25
Journal Article
Recenzirano
Odprti dostop
Although the field of microfluidics has made significant progress in bringing new tools to address biological questions, the accessibility and adoption of microfluidics within the life sciences are ...still limited. Open microfluidic systems have the potential to lower the barriers to adoption, but the absence of robust design rules has hindered their use. Here, we present an open microfluidic platform, suspended microfluidics, that uses surface tension to fill and maintain a fluid in microscale structures devoid of a ceiling and floor. We developed a simple and ubiquitous model predicting fluid flow in suspended microfluidic systems and show that it encompasses many known capillary phenomena. Suspended microfluidics was used to create arrays of collagen membranes, mico Dots (μDots), in a horizontal plane separating two fluidic chambers, demonstrating a transwell platform able to discern collective or individual cellular invasion. Further, we demonstrated that μDots can also be used as a simple multiplexed 3D cellular growth platform. Using the μDot array, we probed the combined effects of soluble factors and matrix components, finding that laminin mitigates the growth suppression properties of the matrix metalloproteinase inhibitor GM6001. Based on the same fluidic principles, we created a suspended microfluidic metabolite extraction platform using a multilayer biphasic system that leverages the accessibility of open microchannels to retrieve steroids and other metabolites readily from cell culture. Suspended microfluidics brings the high degree of fluidic control and unique functionality of closed microfluidics into the highly accessible and robust platform of open microfluidics.
Metapelitic rocks from the northern Prince Charles Mountains-East Amery Ice Shelf region of the Rayner Complex, East Antarctica, record high-temperature reworking during Cambrian times. Calculated ...metamorphic phase diagrams for rocks with varying chemical compositions and mineral assemblages suggest that peak temperatures were 800-870 degree C at pressures of 5.5-6.5 kbar. However, Cambrian-age high-T reworking is patchy and is recorded only in some locations, with other areas recording pristine early Mesoproterozoic-Neoproterozoic assemblages formed during the c. 1000-900Ma Rayner Orogeny. The spatial distribution of reworking may indicate that the comparatively anhydrous residual rock compositions inherited from the Rayner Orogeny were relatively inert to reworking during the Cambrian. Domains that record Cambrian reworking conceivably underwent hydrous retrogression at the end of the Rayner Orogeny and were therefore comparatively reactive during reheating in the Cambrian. High-T reworking during the Cambrian has previously been recognized in the Prydz Bay region at the margin of the Rayner Complex, but not in the northern Prince Charles Mountains. The Eastern Ghats Province in India, which was formerly contiguous with the Rayner Complex, preserves a similarly enigmatic record of Cambrian geochronology, suggesting that the Rayner-Eastern Ghats terrane as a whole may have experienced selective reworking during the Cambrian. The geodynamic setting for the formation of this thermal regime is not well understood, but the attainment of high crustal temperatures may have been facilitated by a reduced capacity for thermal buffering, arising from limited partial melting within a previously dehydrated crustal column.
The synthesis of signaling molecules is one strategy bacteria employ to sense alterations in their environment and rapidly adjust to those changes. In Gram-negative bacteria, bis-(3'-5')-cyclic ...dimeric GMP (c-di-GMP) regulates the transition from a unicellular motile state to a multicellular sessile state. However, c-di-GMP signaling has been less intensively studied in Gram-positive organisms. To that end, we constructed a fluorescent
reporter based on a c-di-GMP-responsive riboswitch to visualize the relative abundance of c-di-GMP for single cells of the Gram-positive model organism
Coupled with cell-type-specific fluorescent reporters, this riboswitch reporter revealed that c-di-GMP levels are markedly different among
cellular subpopulations. For example, cells that have made the decision to become matrix producers maintain higher intracellular c-di-GMP concentrations than motile cells. Similarly, we find that c-di-GMP levels differ between sporulating and competent cell types. These results suggest that biochemical measurements of c-di-GMP abundance are likely to be inaccurate for a bulk ensemble of
cells, as such measurements will average c-di-GMP levels across the population. Moreover, the significant variation in c-di-GMP levels between cell types hints that c-di-GMP might play an important role during
biofilm formation. This study therefore emphasizes the importance of using single-cell approaches for analyzing metabolic trends within ensemble bacterial populations.
Many bacteria have been shown to differentiate into genetically identical yet morphologically distinct cell types. Such population heterogeneity is especially prevalent among biofilms, where multicellular communities are primed for unexpected environmental conditions and can efficiently distribute metabolic responsibilities.
is a model system for studying population heterogeneity; however, a role for c-di-GMP in these processes has not been thoroughly investigated. Herein, we introduce a fluorescent reporter, based on a c-di-GMP-responsive riboswitch, to visualize the relative abundance of c-di-GMP for single
cells. Our analysis shows that c-di-GMP levels are conspicuously different among
cellular subtypes, suggesting a role for c-di-GMP during biofilm formation. These data highlight the utility of riboswitches as tools for imaging metabolic changes within individual bacterial cells. Analyses such as these offer new insight into c-di-GMP-regulated phenotypes, especially given that other biofilms also consist of multicellular communities.
Trace element concentrations in garnet and associated minerals from the mid-Miocene Zhibula Cu skarn, Gangdese Belt, Tibet reflect a diversity of local environments, evolving fluid parameters and ...partitioning with coexisting minerals. Exoskarn occurs as massive but narrow intervals within a Lower Jurassic volcano-sedimentary sequence containing limestone, the main skarn protolith. Endoskarn is present at the contact with mid-Miocene granodiorite dikes. Prograde skarn associations are garnet-dominant but also include diopside-dominant pyroxene in variable amounts. Garnet compositions in exoskarn change from andradite (And)- to grossular (Gr)-dominant from the massive intervals to bands/lenses within marble/tuff, but not in endoskarn. In both cases however, associations at the protolith contact include anorthite and wollastonite, both indicative of skarnoid or distal (relative to fluid source) skarn formation. Exoskarns also contain vesuvianite. Retrograde clinozoisite, actinolite and chlorite replace pre-existing skarn minerals. Garnet displays brecciation and replacement by Al-richer garnet. Depending on partitioning among coexisting minerals, chondrite-normalised REY (REE+Y) fractionation trends for garnet depict endo- to exoskarn diversity, the dominance of And- vs. Gr-rich garnet (in turn related to proximal-to-distal relationship to fluid source), as well as prograde-to-retrograde evolution in the same sample. A strong variation in Eu-anomaly, from positive to negative, in And-dominant garnet can be correlated with variation in salinity of ore-forming fluids, concordant with published fluid inclusion data. Trends depicted by And- and Gr-dominant garnets are consistent with published data from skarns elsewhere, in which the dominant substitution mechanism for REY is YAG-type. Zhibula garnets are enriched in a range of trace elements less commonly reported, including W, Sn, and As, but also Mo (as high as 730ppm), an element seldom analysed for in silicates. Molybdenum, W, and Sn display excellent co-correlation and shared zonation patterns on LA–ICP–MS maps of garnet, indicating substitution in the crystal lattice. As well as assisting in interpreting skarn evolution in time and space, and providing constraints on ore genesis, the trace element data for garnet explain the range of colours observed. The discovery of garnets carrying significant concentrations of W, Sn and Mo is a valuable finding that deserves evaluation in post-collisional skarns elsewhere, and is potentially of critical significance in prospecting. Together with a conspicuous trace ore mineral signature, garnet compositions at Zhibula support a genetic connection and sharing of ore-forming fluids between the skarn and the Qulong porphyry Cu-Mo deposit, 2km to the north. Within the Gangdese belt, or in analogous settings elsewhere, the presence of deep-seated porphyry mineralization beneath exposed skarns could be tested for by studying garnet chemistry. As more data become available, such trace element signatures could be viable tools for distinguishing barren from mineralized skarn systems.
•REY fractionation trends in garnet reflect prograde-to-retrograde evolution.•Garnet chemistry is also controlled by local environment and major oxide content.•Garnet compositions support common fluids for skarn and nearby Cu–Mo porphyry system.•Mo, W and Sn in skarn garnet carry implications for mineral exploration.
•Uranium-bearing hematite is confirmed in Cu-ores from Olympic Dam, South Australia.•U, Mo and W occur within grains displaying oscillatory zonation and porous structures.•The suitability of ...U-bearing hematite for Pb–Pb geochronology was tested.•207Pb–206Pb ages of 1590±8Ma and 1577±5Ma are reported.
Uranium-bearing hematite (containing up to several wt.% U), also containing Al, Mo, W and radiogenic Pb, is described from Olympic Dam, South Australia. These elements are present in grains that display both oscillatory zonation and porous structures. Laser-ablation inductively coupled mass spectrometry (LA-ICP-MS) element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238U- and 206Pb, and are distinct from those of W and Mo. The crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope-focused ion beam technique. Satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long-range superstructure ordering, that is inferred to assist metal incorporation via the substitution 2Fe3+↔Me6++vacancy, where Me=U, W, Mo.
The suitability of U-bearing hematite for Pb–Pb geochronology as a first pass was tested on both zoned and porous hematite grains via LA-ICP-MS, using the GJ-1 zircon as the primary external standard. Only Pb–Pb ages were considered and resulted in 207Pb–206Pb ages of 1590±8Ma and 1577±5Ma for oscillatory and sector zoned hematite from two samples. Although reconnaissance in nature, these ages potentially support the supposition that mineralization is coeval with emplacement of the Gawler Range Volcanics and associated Hiltaba Intrusive Suite. The geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron-bearing ores.
Lipocalins are a superfamily of functionally diverse proteins defined by a well‐conserved tertiary structure despite variation in sequence. Lipocalins bind and transport small hydrophobic molecules ...in organisms of all kingdoms. However, there is still uncertainty regarding the function of some members of the family, including bacterial lipocalin Blc from Escherichia coli. Here, we present evidence that lipocalin Blc may be involved in heme binding, trans‐periplasmic transport, or heme storage. This conclusion is supported by a cocrystal structure, mass‐spectrometric data, absorption titration, and in silico analysis. Binding of heme is observed at low micromolar range with one‐to‐one ligand‐to‐protein stoichiometry. However, the absence of classical coordination to the iron atom leaves the possibility that the primary ligand of Blc is another tetrapyrrole.
The Mount Weld rare earth element (REE) deposit, Western Australia, is one of the largest of its type on Earth. Current mining exploits the high-grade weathered goethite-bearing resource that lies ...above, and which represents the weathering product of a subjacent carbonatite. The mineralogy, petrography, deportment of lanthanides among the different components, and variation in mineral speciation, textures, and chemistry are examined. Microanalysis, involving scanning electron microscope (SEM) imaging, electron probe microanalysis (EPMA) and laser ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS), was conducted on sized fractions of three crushed and ground laterite ore samples from current and planned production, and a representative sample from the underlying carbonatite. High-magnification imaging of particles in laterite samples show that individual REE-bearing phases are fine-grained and extend in size well below the micron-scale. Nanoscale inclusions of REE-phosphates are observed in apatite, Fe-(Mn)-(hydr)oxides, and quartz, among others. These have the appearance, particularly in fluorapatite, of pervasive, ultrafine dusty domains. Apart from the discrete REE minerals and abundant nano- to micron-scale inclusions in gangue, all ore components analysed by LA-ICP-MS contain trace to minor levels of REEs within their structures. This includes apatite, where low levels of REE are confirmed in preserved igneous apatite, but also Fe- and Mn-(hydr)oxides in which concentrations of hundreds, even thousands of ppm are measured. This is significant given that Fe-(Mn)-(hydr)oxides are the most abundant component of the laterite and points to extensive mobility and redistribution of REEs, and especially HREE, during progressive lateritisation. Late-formed minerals, notably tiny grains of cerianite, reflect a shift to oxidising conditions. REE-fluorocarbonates are the main host for REEs in carbonatite and are systematically replaced by hydrated, Ca-bearing REE-phosphates (largely rhabdophane). The latter displays varied compositions but is characteristically enriched in HREE relative to monazite in the same sample. Fine-grained, compositionally heterogeneous rhabdophane is accompanied by minor amounts of other paragenetically late, hydrated phosphates with enhanced MREE/HREE relative to LREE (although still LREE-dominant). Minor, relict xenotime and zircon are significant HREE carriers. Ilmenite and pyrochlore group members contain REE but contribute only negligibly to the overall REE budget. Although the proportions of individual mineral species differ, the chemistry of key ore components are similar in different laterite samples from the current resource. Mineral signatures are, however, subtly different in the lower grade southeastern part of the deposit, including higher concentrations of HREE relative to LREE in monazite, rhabdophane, florencite and Fe-(Mn)-(hydr)oxides.
Compositional data, comprising electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace-element data, are presented for common (Cu)-Pb-Sb ...sulfosalts (bournonite, jamesonite, tetrahedrite, and boulangerite), subordinate semseyite, heteromorphite, robinsonite, and (Cu)-Pb-Bi-Sb sulfosalts, as well as for accompanying base metal sulfides (BMS) in auriferous gold veins from the Gutaishan Au-Sb deposit, southern China. The objectives of the study were to identify whether these sulfosalts represent overlooked hosts for precious metals and other trace elements of petrogenetic or economic interest, establish partitioning trends among coexisting sulfosalt species and between sulfosalts and BMS, and to seek evidence for a genetic link between the abundance of (Cu)-Pb-Sb sulfosalts and the high-fineness of native gold in the deposit. All (Cu)-Pb-Sb sulfosalts analyzed were found to be remarkably poor hosts for gold and thus do not contribute to the overall mineralogical balance for gold. Trace yet measurable concentrations of Au are, however, noted in the (Cu)-Pb-Bi-Sb sulfosalts, in agreement with published data indicating that (Cu)-Pb-Bi-Sb sulfosalts may be minor Au-hosts in some ore systems. Silver is preferentially partitioned into tetrahedrite at the expense of other sulfosalt phases, and tetrahedrite is thus the major host for Ag in the Gutaishan deposit. LA-ICP-MS trace element mapping allows partitioning relationships among different sulfosalt and BMS phases to be determined for several trace elements. Jamesonite concentrates Fe, Zn, Bi, Cd, Ag, Ni, and In over coexisting bournonite, yet boulangerite is the better host for As, Ag, Sn, Se, and Te than jamesonite. Cd and Co are typically enriched in sphalerite relative to any sulfosalt, and when present, pyrite is always enriched in Au and Co relative to all other phases. A high Au/Ag ratio in the ore-forming fluid, the presence of abundant tetrahedrite that has sequestered silver during mineral precipitation, and a lack of evidence for cooling-driven precipitation may be significant reasons for the formation of high-fineness gold throughout the deposit. Two generations of native gold are documented whereby the first is coarse-grained, Ag- and Bi-bearing, and is associated with the main (Cu)-Pb-Sb sulfosalts (bournonite, jamesonite, tetrahedrite, and boulangerite). The second generation is fine-grained and has the highest fineness. Increase in the complexity of sulfosalt assemblages, re-distribution of Ag within coarse native gold and dissolution-reprecipitation reactions among the sulfosalt-gold association increase the gold fineness. The present study shows that linking petrographic aspects at the micrometer-scale with minor/trace element distributions in complex sulfidesulfosalt assemblages can track a complex history of Au deposition and enrichment.
PDF
