Application of multiscale magnetotelluric data to mineral exploration: an example from the east Tennant region, Northern Australia.

The footprint of a mineral system is potentially detectable at a range of scales and lithospheric depths, reflecting the size and distribution of its components. Magnetotellurics is one of a few techniques that can provide multiscale data sets to image and understand mineral systems. We have used long-period data from the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) as a first-order reconnaissance survey to resolve large-scale lithospheric architecture for mapping areas of mineral potential in northern Australia. The 3-D resistivity model reveals a broad conductivity anomaly extending from the Tennant Creek district to the Murphy Province in the lower crust and upper mantle, representing a potential fertile source region for mineral systems. Results from a higher-resolution infill magnetotelluric survey reveal two prominent conductors in an otherwise resistive host whose combined responses result in the lithospheric-scale conductivity anomaly mapped in the AusLAMP model. Integration of the conductivity structure with deep seismic reflection data reveals a favourable crustal architecture linking the lower, fertile source regions with potential depositional sites in the upper crust. The enhanced conductivity likely resulted from the remnant (metallic) material deposited when fluids were present during the 'ancient' tectonic events. This observation strongly suggests that the deep-penetrating major faults potentially acted as pathways for transporting metalliferous fluids to the upper crust where they could form mineral deposits. This result and its integration with other geophysical and geochronological data sets suggest high prospectivity for major mineral deposits in the vicinity of these major faults, that is, Gulunguru Fault and Lamb Fault. In addition to these insights, interpretation of high-frequency magnetotelluric data acquired during the infill survey helps to characterize cover and assist with selecting targets for stratigraphic drilling which, in turn, can validate the models and improve our understanding of basement geology, cover sequences and mineral potential. This study demonstrates that integration of geophysical data from multiscale surveys is an effective approach to scale reduction during mineral exploration in covered terranes with limited geological knowledge.

Lithospheric conductors reveal source regions of convergent margin mineral systems.

The clean energy transition will require a vast increase in metal supply, yet new mineral deposit discoveries are declining, due in part to challenges associated with exploring under sedimentary and volcanic cover. Recently, several case studies have demonstrated links between lithospheric electrical conductors imaged using magnetotelluric (MT) data and mineral deposits, notably Iron Oxide Copper Gold (IOCG). Adoption of MT methods for exploration is therefore growing but the general applicability and relationship with many other deposit types remains untested. Here, we compile a global inventory of MT resistivity models from Australia, North and South America, and China and undertake the first quantitative assessment of the spatial association between conductors and three mineral deposit types commonly formed in convergent margin settings. We find that deposits formed early in an orogenic cycle such as volcanic hosted massive sulfide (VHMS) and copper porphyry deposits show weak to moderate correlations with conductors in the upper mantle. In contrast, deposits formed later in an orogenic cycle, such as orogenic gold, show strong correlations with mid-crustal conductors. These variations in resistivity response likely reflect mineralogical differences in the metal source regions of these mineral systems and suggest a metamorphic-fluid source for orogenic gold is significant. Our results indicate the resistivity structure of mineralized convergent margins strongly reflects late-stage processes and can be preserved for hundreds of millions of years. Discerning use of MT is therefore a powerful tool for mineral exploration.

Lower crustal resistivity signature of an orogenic gold system.

Orogenic gold deposits provide a significant source of the world's gold and form along faults over a wide range of crustal depths spanning sub-greenschist to granulite grade faces, but the source depths of the gold remains poorly understood. In this paper we compiled thirty years of long-period magnetotelluric (MT) and geomagnetic depth sounding (GDS) data across western Victoria and south-eastern South Australia that have sensitivity to the electrical resistivity of the crust and mantle, which in turn depend on past thermal and fluid processes. This region contains one of the world's foremost and largest Phanerozoic (440 Ma) orogenic gold provinces that has produced 2% of historic worldwide gold production. Three-dimensional inversion of the long-period MT and GDS data shows a remarkable correlation between orogenic gold deposits with > 1 t production and a < 20 Ω m low-resistivity region at crustal depths > 20 km. This low-resistivity region is consistent with seismically-imaged tectonically thickened marine sediments in the Lachlan Orogen that contain organic carbon (C), sulphides such as pyrite (FeS2) and colloidal gold (Au). Additional heat sources at 440 Ma due to slab break-off after subduction have been suggested to rapidly increase the temperature of the marine sediments at mid to lower crustal depth, releasing HS- ligands for Au, and CO2. We argue that the low electrical resistivity signature of the lower crust we see today is from a combination of flake graphite produced in situ from the amphibolite grade metamorphism of organic-carbon in the marine sediments, and precipitated graphite through retrograde hydration reactions of CO2 released during the rapid heating of the sediments. Thus, these geophysical data image a fossil source and pathway zone for one of the world's richest orogenic gold provinces.

The efficacy of a voice training program: a case-control study in China.

The objective of this study was to design a voice training program for Chinese speakers, and to evaluate its efficacy. It was a prospective, randomized, case-control study practiced in three middle schools in Beijing, China. Teachers in the treatment group received voice training for 4 weeks, whereas the control group subjects received no treatment. The voice training program, which was adapted for Chinese, contained vocal hygiene education and group voice training. The outcome was assessed by voice handicap index (VHI), maximum phonation time (MPT) and acoustic analysis parameters including, noise to harmonic ratio (NHR), jitter and shimmer. The results showed that at the onset of the study, no significant differences were found between the subjects in two groups for VHI, MPT and NHR. VHI of treatment group subjects who received voice training decreased significantly, whereas VHI of control group subjects showed no significant change. Treatment group MPT was significantly increased after training, whereas the control group one presented no significant change during the same period. NHR in treatment group decreased significantly after training, whereas the one in control group showed no significant change. There were no significant changes for jitter and shimmer in both groups before and after the study. So we conclude that the voice training program is suitable to treat voice diseases, particularly for middle school teachers. This result provided reliable evidence for carrying out further voice training in China.

[Study of voice changes pre- and post-tonsillectomy].

OBJECTIVE: To evaluate changes in acoustic features of voice after tonsillectomy. METHOD: Thirty-three patients presenting for tonsillectomy were recruited. Voice recordings obtained from patients before and 1 month after surgery, were analyzed using the Kay Elemetrics, multi-dimensional voice processing software. The following parameters were estimated: the first formant (F1, B1), average of fundamental frequency (F0), Jitter percent (Jitter), Shimmer, noise-to-harmonics ratio (NHR). RESULT: There were significant difference in the first formant frequency and bandwidth before and 1 month after surgery. The larger the tonsil was, the more changes were seen in the formant frequency. No significant differences were found for F0, Jitter, Shimmer, NHR decreased after the surgery. CONCLUSION: The modifications in the anatomical structure and volume of the vocal tract, induced by the tonsillectomy can change the formant frequency and bandwidth. The larger the tonsil was, the more changes were detected in the formant frequency.

[Effectiveness of voice training for professional voice users with voice disorders].

OBJECTIVE: To explore the effectiveness of voice training on professional voice users with voice disorders. METHODS: Thirty one professional voice users suffering from voice symptoms without organic disorder were treated with a four-week voice training program, including vocal hygiene education, respiratory training and resonant therapy. Voice handicap index, maximum phonation time, noise to harmonic ratio, jitter and shimmer were compared before and after the training. RESULTS: The voice handicap index (x(-) ± s) decreased from 33.7 ± 19.2 to 18.8 ± 18.4 after the training and the difference was significant (t = 6.14, P < 0.05). Maximum phonation time (x(-) ± s) increased significantly from (15.5 ± 5.8) s to (18.6 ± 6.0) s (t = -3.43, P < 0.05). jitter (M [P(25); P(75)]) decreased significantly after the training from 0.42% [0.36%; 0.62%] to 0.35% [0.29%; 0.47%] (Z = -2.51, P < 0.05), while there was no significant change in shimmer and noise to harmonic ratio. CONCLUSION: Voice training can effectively reduce the vocal symptoms in professional voice users, decrease the handicap degree and increase the respiratory support during phonation, thus improve the voice quality.

[Analysis of misdiagnosis and differential diagnosis of infectious mononucleosis in adults].

OBJECTIVE: To explore the clinical characteristics of infectious mononucleosis (IM) in adults. METHOD: Medical records of 50 adult IM patients admitted in hospital were analyzed retrospectively. RESULT: Diagnosis delayed group contained 16 patients (32% of total patients) and was significantly different from the diagnosis in-time group in typical symptoms, signs and laboratory findings of IM. CONCLUSION: The clinical manifestations of adult IM are rather complicated and nonspecific to diagnosis. History collection and physical examination in detail are helpful for early diagnosis.