Michael Verrall

Naturally occurring gold nanoparticles and nanoplates

During the weathering of gold deposits, exceptionally pure, <200 nm diameter, nanoparticulate gold plates (6 nm thick) are formed. The particles display controlled growth of both size and shape and signs of assembly to form belts and sheets. The gold is associated and intergrown with minerals formed by evaporation and is interpreted to have been deposited rapidly from saline groundwater during a drying event. The size and morphology of the gold nanoparticles and nanoplates are identical to the products of experimentally manufactured gold colloids. This represents the fi rst direct observation of colloidal nanoparticulate gold in nature, confi rming this as an active mechanism of gold transport during the weathering of gold deposits.

Mineralogy and crystal chemistry of “garnierites” in the Goro lateritic nickel deposit, New Caledonia

The mineralogy and crystal chemistry of “garnierites” in saprolitic ore from the Goro lateritic nickel deposit, New Caledonia, was investigated using optical and scanning electron microscopy, X-ray diffraction (XRD) and electron-microprobe analyses. These conspicuously, green-coloured phases occur either as sub-mm to cm-sized veins or as macroscopic (sub-cm sized) “booklets”. Veins comprised ~ 10 A (2:1) talc-like minerals identified as species of the Ni-kerolite/pimelite Ni for Mg solid solution series, with Ni contents ranging from 10 to 24 % NiO. Mineral nomenclature, defined by the inverse relationship between Ni and Mg content, varied continuously over the scale of several hundred micrometres. Pimelite, defined as containing > 1.5 Ni per formula unit (p.f.u.), was the main 10 A phase for one vein core whereas at the vein edges where the Ni content decreased to < 1.5 Ni p.f.u. (and Mg increased) kerolite was identified. “Booklets” comprised the ~ 7 A (1:1) serpentine-like phase, nepouite (Mg0.67Ni1.59Fe0.053+) (Si2.17Al0.22)O5(OH)4 with Ni contents averaging 30 % NiO and occurred as accordion-like structures supported in an undifferentiated matrix of mixed ~ 7 A and ~ 10 A phases.

Distribution of Metals in the Termite Tumulitermes tumuli (Froggatt): Two Types of Malpighian Tubule Concretion Host Zn and Ca Mutually Exclusively

The aim of this study was to determine specific distribution of metals in the termite Tumulitermes tumuli (Froggatt) and identify specific organs within the termite that host elevated metals and therefore play an important role in the regulation and transfer of these back into the environment. Like other insects, termites bio-accumulate essential metals to reinforce cuticular structures and utilize storage detoxification for other metals including Ca, P, Mg and K. Previously, Mn and Zn have been found concentrated in mandible tips and are associated with increased hardness whereas Ca, P, Mg and K are accumulated in Malpighian tubules. Using high resolution Particle Induced X-Ray Emission (PIXE) mapping of whole termites and Scanning Electron Microscope (SEM) Energy Dispersive X-ray (EDX) spot analysis, localised accumulations of metals in the termite T. tumuli were identified. Tumulitermes tumuli was found to have proportionally high Mn concentrations in mandible tips. Malpighian tubules had significant enrichment of Zn (1.6%), Mg (4.9%), P (6.8%), Ca (2.7%) and K (2.4%). Synchrotron scanning X-ray Fluorescence Microprobe (XFM) mapping demonstrated two different concretion types defined by the mutually exclusive presence of Ca and Zn. In-situ SEM EDX realisation of these concretions is problematic due to the excitation volume caused by operating conditions required to detect minor amounts of Zn in the presence of significant amounts of Na. For this reason, previous researchers have not demonstrated this surprising finding.

Palaeobiology of red and white blood cell-like structures, collagen and cholesterol in an ichthyosaur bone

Carbonate concretions are known to contain well-preserved fossils and soft tissues. Recently, biomolecules (e.g. cholesterol) and molecular fossils (biomarkers) were also discovered in a 380 million-year-old concretion, revealing their importance in exceptional preservation of biosignatures. Here, we used a range of microanalytical techniques, biomarkers and compound specific isotope analyses to report the presence of red and white blood cell-like structures as well as platelet-like structures, collagen and cholesterol in an ichthyosaur bone encapsulated in a carbonate concretion from the Early Jurassic (~182.7 Ma). The red blood cell-like structures are four to five times smaller than those identified in modern organisms. Transmission electron microscopy (TEM) analysis revealed that the red blood cell-like structures are organic in composition. We propose that the small size of the blood cell-like structures results from an evolutionary adaptation to the prolonged low oxygen atmospheric levels prevailing during the 70 Ma when ichthyosaurs thrived. The δ13C of the ichthyosaur bone cholesterol indicates that it largely derives from a higher level in the food chain and is consistent with a fish and cephalopod diet. The combined findings above demonstrate that carbonate concretions create isolated environments that promote exceptional preservation of fragile tissues and biomolecules.

The dynamics of gold in regolith change with differing environmental conditions over time

Significant Au discoveries are becoming less common because the remaining prospective, underexplored areas are obscured by transported cover. At Moolart Well (Western Australia), secondary Au deposits hosted in transported pisolitic ferricrete and saprolite are overlain by younger transported cover. Here, we show how Au has been, and is being, dispersed and concentrated in these deposits and the overlying younger transported cover and biota during the evolution of the landscape. We identified coarse (>400 µm), Ag-rich, primary, angular Au accumulated residually along with some precipitated, Ag-poor ( Acacia aneura ) and termite mounds indicates active dispersion.

Generation of amorphous carbon and crystallographic texture during low-temperature subseismic slip in calcite fault gouge

Identification of the nano-scale to micro-scale mechanochemical processes occurring during fault slip is of fundamental importance to understand earthquake nucleation and propagation. Here we explore the micromechanical processes occurring during fault nucleation and slip at subseismic rates (∼3 × 10−6 m s–1) in carbonate rocks. We experimentally sheared calcite-rich travertine blocks at simulated upper crustal conditions, producing a nano-grained fault gouge. Strain in the gouge is accommodated by cataclastic comminution of calcite grains and concurrent crystal-plastic deformation through twinning and dislocation glide, producing a crystallographic preferred orientation (CPO). Continued wear of fine-grained gouge particles results in the mechanical decomposition of calcite and production of amorphous carbon. We show that CPO and the production of amorphous carbon, previously attributed to frictional heating and weakening during seismic slip, can be produced at low temperature during stable slip at subseismic rates without slip weakening.