Electronic damage in S atoms in a native protein crystal induced by an intense X-ray free-electron laser pulse

Current hard X-ray free-electron laser (XFEL) sources can deliver doses to biological macromolecules well exceeding 1 GGy, in timescales of a few tens of femtoseconds. During the pulse, photoionization can reach the point of saturation in which certain atomic species in the sample lose most of their electrons. This electronic radiation damage causes the atomic scattering factors to change, affecting, in particular, the heavy atoms, due to their higher photoabsorption cross sections. Here, it is shown that experimental serial femtosecond crystallography data collected with an extremely bright XFEL source exhibit a reduction of the effective scattering power of the sulfur atoms in a native protein. Quantitative methods are developed to retrieve information on the effective ionization of the damaged atomic species from experimental data, and the implications of utilizing new phasing methods which can take advantage of this localized radiation damage are discussed

Coherent diffractive imaging of microtubules using an X-ray laser

X-ray free electron lasers (XFELs) create new possibilities for structural studies of biological objects that extend beyond what is possible with synchrotron radiation. Serial femtosecond crystallography has allowed high-resolution structures to be determined from micro-meter sized crystals, whereas single particle coherent X-ray imaging requires development to extend the resolution beyond a few tens of nanometers. Here we describe an intermediate approach: the XFEL imaging of biological assemblies with helical symmetry. We collected X-ray scattering images from samples of microtubules injected across an XFEL beam using a liquid microjet, sorted these images into class averages, merged these data into a diffraction pattern extending to 2 nm resolution, and reconstructed these data into a projection image of the microtubule. Details such as the 4 nm tubulin monomer became visible in this reconstruction. These results illustrate the potential of single-molecule X-ray imaging of biological assembles with helical symmetry at room temperature

Gold mineralization in the Mazowe area, Harare-Bindura-Shamva greenstone belt, Zimbabwe: I. Tectonic controls on mineralization

The Mazowe group of mines (principal mines Mazowe, Bernheim and Stori's Golden Shaft) is situated within the Harare-Bindura-Shamva greenstone belt of the Zimbabwean Archaean craton, west of the Chinamora batholith. Gold mineralization in the form of quartz (±sulfide) reefs is structurally controlled in reverse shear zones that dip moderately north at Mazowe mine, and conjugate steep strike-slip shear zones striking WNW (dextral) and NE (sinistral) at Bernheim and Stori's Golden Shaft mines. The syn-mineralization deformation (D2/3) in all the mines has a northerly shortening direction. This deformation is compatible with the regional late Archaean D2/3 event, which agrees with late Archaean ages determined for the host rocks and for the mineralization. The mineralization cannot be related to any major regional scale shear zones, and it is incompatible with strains related to the intrusion of either the Chinamora batholith or internal granitoid suites. These observations show that significant gold deposits can form in relatively minor deformation events, unrelated to either major shear zones or granitoid intrusions

High CO2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: A new category of ore forming fluids?

Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Abosso/Damang and Ayanfuri gold deposits in the Ashanti Belt, Ghana. Primary fluid inclusions in quartz from mineralised veins of the Ashanti, Prestea, Konongo-Southern Cross, and Abosso/Damang deposits contain almost exclusively volatile species. The primary setting of the gaseous (i.e. the fluid components CO2, CH4 and N2) fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids. Microthermometric and Raman spectroscopic analyses of the inclusions revealed a CO2 dominated fluid with variable contents of N2 and traces of CH4. Water content of most inclusions is below the detection limits of the respective methods used. Aqueous inclusions are rare in all samples with the exception of those from the granite-hosted Ayanfuri mineralisation. Here inclusions associated with the gold mineralisation contain a low salinity ( CO2 and low salinity ( ±  6 eq.wt.%NaCl). However, fluid inclusions in quartz from the gold mineralisations in the Ashanti belt point to distinctly different fluid compositions. Specifically, the predominance of CO2 and CO2 >> H2O have to be emphasized. Fluid systems with this unique bulk composition were apparently active over more than 200␣km along strike of the Ashanti belt. Fluids rich in CO2 may present a hitherto unrecognised new category of ore-forming fluids

Precise U-Pb mineral ages, Rb-Sr and Sm-Nd systematics for the Great Dyke, Zimbabwe - constraints on late Archean events in the Zimbabwe craton and Limpopo belt

U–Pb dating of zircon and rutile from bronzitites of the P1 pyroxenite layer of the Great Dyke precisely constrains the crystallization age of this part of the intrusion to 2575.4±0.7 Ma. Whole rock Rb–Sr and Sm–Nd data of various rock types sampled along the entire length of the Great Dyke record inhomogeneous initial isotope ratios, and also later (<1.5 Ga) disturbances of the Rb–Sr and Sm–Nd isotope systems. The 2575.4±0.7 Ma emplacement age of the Great Dyke is ≈120 Ma older than assumed until recently, and calls for new interpretations of the crustal development of the Zimbabwe craton. Close temporal links between the intrusion of the Great Dyke and the emplacement of late Archean granitoids (Chilimanzi and Razi suites) of the Zimbabwe craton are indicated by the new precise age data. The Chilimanzi and Razi suites of granitoids form at least two sub-suites, which can be described as pre- and post-Great Dyke in age. The Great Dyke age now falls within the range of ages for tectonic events in the Limpopo belt including granitoid magmatism, metamorphism, and thrusting of the Northern Marginal Zone over the Zimbabwe craton. A west-to-east diachroneity in both thrusting and crustal stabilization is suggested by the observations that the Great Dyke cuts across the thrust in the west, but syn-tectonic granitoids that are younger than the Great Dyke are deformed by the thrusting in the east. Intrusion of the Great Dyke cannot be linked to collision of the Zimbabwe and Kaapvaal cratons. The overlap in ages of intrusion of the Great Dyke and late Archean events in the Zimbabwe craton shows that Archean crust was cratonized shortly after large-scale melting and granite intrusion