Diversity of supergene gold expressions and implications for gold targeting in an equatorial regolith (AMG’s Couriège exploration prospect, French Guiana)

The Couriège prospect (French Guiana) provides key examples of the diversity of gold distribution related to supergene processes. The nature of gold in two contrasted weathering profiles is examined as a function of the weathering lithofacies. The autochthonous profile hosts weathered Au-bearing quartz veins whereas the pediment profile is enriched in free gold issued from dismantled gold-bearing quartz veins. The gold distribution is controlled by: (i) the preservation of primary gold as free gold in both transported and autochthonous horizons and as electrum inclusions in detrital pyrite, and (ii) the formation of secondary gold through dissolution/precipitation processes, expressed as gold spherulites on free gold grain surface, Ag-depleted rim around transported free gold grains and Ag-depleted gold micro-inclusions hosted by oxidised autochthonous pyrite. Gold enrichment through supergene chemical processes remains limited within the truncated autochthonous profile. A new conceptual model is proposed for the area, defining the role of chemical and physical processes in gold endowment, and accounting for the geomorphological context. The overall evolution includes (i) deep weathering and peneplenation, (ii) dismantlement and transport of lateritic material, and (iii) development of a latosol cover. This study highlights that gold exploration in tropical environments must consider the residual vs transported nature and the inheritance of targeted pedogenic horizons.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5476187

Anticancer effects against colorectal cancer models of chloro(triethylphosphine)gold(I) encapsulated in PLGA–PEG nanoparticles

Chloro(triethylphosphine)gold(I), (Et3PAuCl hereafter), is an Auranofin (AF)-related compound showing very similar biological and pharmacological properties. Like AF, Et3PAuCl exhibits potent antiproliferative properties in vitro toward a variety of cancer cell lines and is a promising anticancer drug candidate. We wondered whether Et3PAuCl encapsulation might lead to an improved pharmacological profile also considering the likely reduction of unwanted side-reactions that are responsible for adverse effects and for drug inactivation. Et3PAuCl was encapsulated in biocompatible PLGA–PEG nanoparticles (NPs) and the new formulation evaluated in colorectal HCT-116 cancer cells in comparison to the free gold complex. Notably, encapsulated Et3PAuCl (nano-Et3PAuCl hereafter) mostly retains the cellular properties of the free gold complex and elicits even greater cytotoxic effects in colorectal cancer (CRC) cells, mediated by apoptosis and autophagy. Moreover, a remarkable inhibition of two crucial signaling pathways, i.e. ERK and AKT, by nano-Et3PAuCl, was clearly documented. The implications of these findings are discussed.

A simple AuNPs-based colorimetric aptasensor for chlorpyrifos detection

Background Chlorpyrifos (Chl) is an organophosphorus pesticide, which has toxicity to environment, animals and human beings. To overcome the shortages of traditional detection methods of small molecular, this study aimed to develop a sensitive, simple, low cost and on-site rapid method for Chl analysis and detection. Thus, we developed a simple label-free gold nanoparticles (AuNPs) based colorimetric biosensor aptasensor for Chl detection using an aptamer as the caputure probe. Results The Chl-aptamer with low dissociation constant (Kd) of 58.59 ± 6.08 (nM) was selected by ssDNA library immobilized systematic evolution of ligands by enrichment (SELEX). In the absence of Chl, the Chl-aptamer acted as the stabilizer for AuNPs in salt solution. In the presence of Chl, the highly specific Chl-aptamer bound with Chl targets immediately thus a self-aggregation of AuNPs induced by salt was displayed. The fabricated colorimetric aptasensor exhibited an excellent sensitivity for Chl detection with the limit of detection as low as 14.46 nM. In addition, the aptasensor was applied to test Chl in tap water, cucumber and cabbage samples, which showed satisfying results with excellent recovery values between 96.2% and 105.6% and acceptable RSD values below 5%. Conclusions The developed colorimetric aptasensor can serve as a promising candidate for Chl detection in the area of biosensors, which also showed a great potential in simple, cheap and rapid detection of Chl.

Key Role of π–π Complex in Diary Cross-Coupling between Aryldiazonium Salts and Arylboronic Acids using Photosensitizer-Free Gold/Photoredox Catalysis

DFT and TD-DFT calculations were performed to better understand the photosensitizer-free visible-light-mediated Au-catalyzed cross-couplings between aryldiazonium salts and arylboronic acids. The π–π type complex between the aryldiazonium salt and the...

Prospects for Degdekan Gold Project in the North-East of Russia

The article describes the analytical, mineralogical and technological studies into enclosing rocks of Degdekan gold deposit. It is found that ore composition is dominated by silicon oxide (62.2–70.4 %), the ore-forming minerals are mainly iron, sulfur and arsenic in sulfide and oxide forms. The clustering analysis distinguishes three representative geochemical associations: Au-Ag-Pb-Sb; As-Mo-Cu; Co-Ni-Cr-Zn-W. Mineralization is pyrite, arsenopyrite, free gold, seldom fahlore, pyrrhotine, chalcopyrite, galena, sphalerite, etc. Pyrite contains As and Ni impurities. By the criteria of association and recovery, gold is present in 4 varieties: free gold recoverable by amalgamation and cyanation; fine gold associated with sulfides and disengageable after oxidizing roasting; fine and very fine gold associated with iron hydroxides, carbonates and chlorites, and extractable in cyanation after HCl treatment; fine gold associated with carbon black and recoverable by cyanation after oxidating roasting at a temperature of 650 °C. The bulk (from 41.6 to 86 %) is represented by free gold extractable in cyanation and gravity separation. This gold features large particles and occurs at the zones of quartz veins, both in veins and in strings. Percentage of fine gold (–0.04 mm) in metasomatic quartz–cericite rocks (nearby veins) varies from 2 to 11 %. There are also platinoid group metals, highly concentrated in sulfide concentrates. Potential resources of platinoids as associated metals are estimated as 10 t (around 10 % of gold resources). The authors arrive at the conclusion on feasibility of joint concentration of gold and platinoids in an integrated process circuit by gravity separation with end product as a Doré bar containing platinoids.