Dispersed Gold and Associated Disseminated Mineralization of Leucogranites of the Dukat Ore Field as Indicators of the Generation Conditions of Magmatogene Gold-Bearing Fluids

—We present data on dispersed gold and associated disseminated mineralization of leucogranites controlling the location of the Dukat epithermal Au–Ag deposit. The data suggest the formation and burial of small portions of oversaturated gold-bearing fluids in hypabyssal magmatic bodies. The lower (relative to silver) contents of gold in the deposit ores and the high Ag/Au ratios (350–550) are due to the limited occurrence of oxidized gold-bearing fractions of magmatogene fluids. This limitation is explained by the active interaction of late magmatic portions of fluids and the material of the host carbonaceous volcanosedimentary unit and by the formation of an environment favorable for the concentration, migration, and deposition of manganese, silver, and nonferrous-metal compounds.

Gold Nanoparticles Functionalized with Mercaptosuccinic Acid as a Means for Detecting Fe(III) Ions

The application of mercaptosuccinic acid-capped gold nanoparticles as a sensing probe for the colorimetric detection of Fe(III) is reported. The well-dispersed gold nanoparticles (AuNPs) with a diameter of around 20 nm were obtained by a one-step reaction of tetrachloroauratic acid with mercaptosuccinic acid (MSA) as a reducing and capping agent, respectively. Fe(III) reportedly causes the aggregation of prepared MSA-capped AuNPs followed by a change in color and a shift to long wavelengths in the absorbance spectra. The resulting method allows for a visual and spectrophotometric Fe(III) determination with detection limits of 30 ng/mL and 23 ng/mL, respectively. MSA-capped AuNPs have been used as sensing probes for the detection of Fe(III) in drinking water samples with a detection limit that is much lower than the maximum permissible level of Fe(III) specified by official regulations (300 ng/mL).

Microgel that swims to the beat of light

Complementary to the quickly advancing understanding of the swimming of microorganisms, we demonstrate rather simple design principles for systems that can mimic swimming by body shape deformation. For this purpose, we developed a microswimmer that could be actuated and controlled by fast temperature changes through pulsed infrared light irradiation. The construction of the microswimmer has the following features: (i) it is a bilayer ribbon with a length of 80 or 120 $$\upmu $$ μ m, consisting of a thermo-responsive hydrogel of poly-N-isopropylamide coated with a 2-nm layer of gold and equipped with homogeneously dispersed gold nanorods; (ii) the width of the ribbon is linearly tapered with a wider end of 5 $$\upmu $$ μ m and a tip of 0.5 $$\upmu $$ μ m; (iii) a thickness of only 1 and 2 $$\upmu $$ μ m that ensures a maximum variation of the cross section of the ribbon along its length from square to rectangular. These wedge-shaped ribbons form conical helices when the hydrogel is swollen in cold water and extend to a filament-like object when the temperature is raised above the volume phase transition of the hydrogel at $$32\,^{\circ } \hbox {C}$$ 32 ∘ C . The two ends of these ribbons undergo different but coupled modes of motion upon fast temperature cycling through plasmonic heating of the gel-objects from inside. Proper choice of the IR-light pulse sequence caused the ribbons to move at a rate of 6 body length/s (500 $$\upmu $$ μ m/s) with the wider end ahead. Within the confinement of rectangular container of 30 $$\upmu $$ μ m height and 300 $$\upmu $$ μ m width, the different modes can be actuated in a way that the movement is directed by the energy input between spinning on the spot and fast forward locomotion. Graphic abstract

Geochemical Features of the Tulallar Gold Ore Field

The article discusses the geochemical features of the Tulallar gold field in the Lesser Caucasus. Distributions of gold and accompanying elements (Ag, As, Hg, Bi, Cu, Zn) in metasomatically altered rocks taken from mine workings (ditches, adits, etc.) and wells are considered. The results of analyzes of furrow samples showed that the content of Au ranges from 0.4 ppm to 37.5 ppm, Ag - from 0.5 ppm to 48.4 ppm. In strongly kaolinized, weakly limonitized quartzites, the Au content ranged from 0.4 to 1.2 ppm, Ag - from 4.0 to 8.8 ppm. In the well drilled in the Central Block, closer to the surface, the siliceous breccias contain Au 309-363 ppm, Ag 132-250 ppm, and high As, Bi and Hg contents are also noted. A similar picture is observed in the silicified rocks of the wells of the Western block. Correlations between Au, Ag and other impurity elements were determined using the STAT program. A direct positive correlation has been established between Au and Ag, Au and Bi, Au and Hg. A positive relationship was also found between Ag and Bi, Ag and Hg. Cluster analysis revealed two different mineral associations: 1) native elements and their compounds - minerals and 2) polysulfide. The closest connection is observed between Ag, Hg and Au. Mineralogically, the Ag-Hg-Au-Bi cluster apparently corresponds to an early ore association - electrum, bismuth tellurides, possibly with inclusions of finely dispersed gold. The second, polymetallic cluster is characterized by a weak correlation bond Аs-Сu-Zn, which indicates that polysulfides were deposited later. The largest amount of Au was deposited in the early mineral association.

A highly sensitive electrochemical microRNA-21 biosensor based on intercalating methylene blue signal amplification and a highly dispersed gold nanoparticles/graphene/polypyrrole composite

An ultrasensitive electrochemical biosensor based on a gold nanoparticles/graphene/polypyrrole composite modified electrode and a signal amplification strategy employing methylene blue is developed as a potential tool for the detection of miRNA-21.

Deposition of highly dispersed gold nanoparticles onto metal phosphates by deposition-precipitation with aqueous ammonia

An efficient method for depositing gold nanoparticles onto metal phosphate has been developed. Deposition-precipitation with aqueous ammonia enabled small gold nanoparticles to be deposited onto a series of metal phosphates...

Atomically Dispersed Gold Anchored on Carbon Nitride Nanosheets as Effective Catalyst for Regioselective Hydrosilylation of Alkynes

The hydrosilylation of alkynes is a powerful process for producing vinylsilane compounds, which are synthetically versatile organosilicon reagents in organic chemistry. Herein, atomically dispersed Au anchored on g-C3N4 nanosheets is...