University of Leoben Department of Applied Geosciences Geology of the Fanjiabauzi Talc Deposit, Liaoning Province, China by David Misch, BSc Eidesstattliche Erklärung Ich erkläre an Eides statt, dass ich diese Arbeit selbstständig verfasst, andere als die angegebenen Quellen und Hilfsmittel nicht benutzt und mich auch sonst keiner unerlaubten Hilfsmittel bedient habe. Affidavit I declare in lieu of oath, that I wrote this thesis and performed the associated research myself, using only literature cited in this volume. Leoben, September 2012 David Misch Abstract The talc deposits of China are world class concerning size and quality of mineralization. The largest deposit of China is located near the village of Mafeng in the Eastern Liaoning Province (Fanjiabauzi). Mineralizations of talc occur in Early Proterozoic Mg-rich carbonates. The region also hosts some of the world’s largest magnesite deposits. Talc from Fanjiabauzi is remarkably pure and shows only minor impurities compared to other deposit types, especially compared to alpine talc deposits. Genesis of talc and host rock was heavily discussed in the past, new data concerning rock chemistry, isotopic composition and composition of fluid inclusions strengthens the widespread thesis of primary magnesite formation in an Early Proterozoic, shallow marine or lagoonal environment with significant freshwater influence. Later multiple deformation events formed large, high-quality magnesite marble deposits along an E-W-trending belt in the Eastern Liaoning Province. The age of hydrothermal talc formation responsible for the high-quality talc deposit of Fanjiabauzi remains unclear, as the deformation history in the region is very complex. Multiple deposit forming processes occurred in several mineralization periods throughout the geologic history from the Early Proterozoic until the young Himalayan orogenic event. Nevertheless, chemical analysis of talc shows no evidence for multiple generations of talc formation. Several other hydrothermal deposits in the Eastern Liaoning Province are attributed to the Triassic (Indosinian) metallogenic period, correlation of the Fanjiabauzi deposit with other locations in the region requires further investigation. i Zusammenfassung Die Talk-Vorkommen Chinas zählen zu den weltweit bedeutendsten Talk- Lagerstätten hinsichtlich Qualität und Größe der Mineralisation. Einige der wichtigsten chinesischen Talk-Lagerstätten befinden sich im sogenannten Haicheng- Dashiqiao-Talk-Magnesit-Belt im Nordosten des Landes. Hier ist auch die Talklagerstätte Fanjiabauzi lokalisiert. Talk wurde hier in Mg-reichen Karbonaten des frühen Proterozoikums im Zuge hydrothermaler Alteration des Nebengesteins gebildet. Neben Talk befinden sich auch einige weltweit bedeutende Magnesitlagerstätten innerhalb des Haicheng-Dashiqiao-Belts. Eine Besonderheit des Talks aus Fanjiabauzi ist die außerordentliche Reinheit und der hohe Weißegrad des Produkts im Vergleich zu anderen Lokalitäten. Die Magnesitgenese ist bis heute Teil heftiger Kontroversen, das häufig vertretene syngenetisch-sedimentäre Bildungsmodell steht einem epigenetisch-metasomatischen Ansatz gegenüber. Die in dieser Arbeit gesammelten Daten sprechen für das syngenetisch-sedimentäre Modell, welches traditionell als Erklärung der außergewöhnlich mächtigen Magnesitabfolgen der Region herangezogen wird. Isotopenverteilung, Spurenelementgehalte und Zusammensetzung von Flüssigkeitseinschlüssen aus dem Magnesit sprechen für ein frühproterozoisches, flachmarines Bildungsmilieu mit signifikantem Süßwassereinfluss. Spuren biogener Aktivität (Stromatolithen) sowie sedimentäre Marker wie Trockenrisse bestätigen dieses Modell. Spätere Metamorphoseevents führten zu einer nahezu vollständigen Rekristallisation des primären Magnesitsediments, dieser Prozess ist für die Bildung der bedeutenden Magnesitlagerstätten des E-W-streichenden Haicheng-Dashiqiao-Belts verantwortlich. Bildungszeitraum und Genesemodell der Talkvorkommen der östlichen Liaoning-Provinz sind weiterhin nicht eindeutig geklärt. Grund dafür ist die komplexe metamorphe Tektonik in der Region. Lagerstättenbildende Prozesse fanden laufend statt und sind in verschiedenen metallogenetischen Perioden vom frühen Proterozoikum bis zur jungen Himalaya-Orogenese eingeteilt. Viele hydrothermale Lagerstätten der Region werden der triassischen (indosinischen) Vererzungsperiode zugeordnet, eine Korrelation von Fanjiabauzi mit anderen Lokalitäten und Vererzungstypen bekannten Bildungsalters erfordert weitere Untersuchungen. Die chemische Elementverteilung ausgewählter Talkproben spricht nicht für mehrere Generationen der Talkbildung. ii Project summary The chemical and structural analysis of the Aihai talc deposit confirmed the impression of the 2009 fieldwork. The talc shows exceptionally high quality and purity, which is almost unique worldwide. The Haicheng talc deposit is stated as the world’s largest talc deposit by Chinese mining authorities. The chemical analysis of the talc samples collected during the 2010 field work shows very low grades of contamination with trace minerals like mica, also the values for trace elements embedded in the talc structure are very low especially for the grade 1 talc product. This causes the remarkably high grades of whiteness and the low LOI values for the grade 1 samples. The LOI is about 3 to 5 percent higher for grade 2 talc samples; the reason for this increase of volatile components is a higher content of carbonate minerals like magnesite and dolomite, which lose their CO 2 during heating. This higher carbonate content is also proved by higher CaO and MgO values for the average grade 2 talc. The contents of other trace elements like FeO and Al 2O3 are also slightly higher in the average grade 2 talc, although the values in general are typically low, which can be expected for carbonate host talc deposits. These values are mostly controlled by mineral impurities, for example mica or other mineral components, which were mechanically integrated in the talc shear zones. The elements Co, Ni, Cr, Cu and W are throughout under the detection limit, this again proves the absence of ultramafic rocks during the primary talc formation. The only mafic components present at the Aihai talc mine are lamprophyre dykes which are younger than the talc formation and mostly do not influence the quality of the deposit. Only in some parts of the deposit, some dyke components are included into small talc bodies because of tectonic movement. This occurrence does not affect the quality of the mineable talc. The host rock of the talc deposit consists mostly of magnesitic and dolomitic marble, the magnesite marble shows some interesting characteristics which allow to draw conclusions if major amounts of talc are present in the nearest environment. In general, the marble in the direct neighborhood of remarkable talc bodies shows a higher purity. There is less contamination with other mineral components like mica, although this pollution is also very minor for magnesite without talc in the nearest environment. This difference is proved by slightly lower Al and Sr values for the talc- iii host magnesite samples. The values for trace elements included into the magnesite crystal lattice also show a decrease when a talc shear zone with a size relevant for production is close to the sampling spot. The values for Mn, Fe and Ca show the same trend, the reason for the higher Ca contents in non-talc magnesite most likely is caused by small amounts of dolomite admixed with the magnesite rock. Therefore, increasing dolomite contents could indicate the departure from the nearest deposit environment. In summary, the higher purity of talc-hosting magnesite in comparison to magnesite without talc in the direct neighborhood is evident and represents the influence of late hydrothermal activity, coherent with the actual talc formation in the older magnesite belt. The differences in the chemical composition could be helpful for the detection of mineable talc in the actual mining levels, although this can only be an additional support for traditional exploration and requires a constant sampling and testing procedure. Another potential indicator for talc shear zones is the texture and coloration of the host rock. The magnesite at the borders of large talc bodies has a bright white coloration and a fine-grained, compact fabric. The magnesite occurring further away from the deposit borders has often a slightly grey coloration and a coarser grained fabric, dolomite occurs often away from the deposit borders whereas at the borders pure magnesite dominates. This correlates with the higher Ca and Fe content of the host rock samples, higher Ca values away from the deposit are caused by dolomite, higher Fe is likely to be caused by pyrite impurities which are common in dolomite but do not occur widespread in the pure magnesite. The genetic processes involved in the deposition of massive Archean carbonate beds in the Eastern Liaoning Province are heavily discussed. Fluid inclusion chemism and isotopic composition of magnesite marble from Fanjiabauzi indicate that the carbonate beds were deposited in a lagoonal to shallow marine evaporitic environment, with significant freshwater dilution. Later hydrothermal and metamorphic processes modified fluid and mineral chemism as well as the isotopic composition of the host rock. This gives reason for different interpretations concerning the deposit formation and later development of the regional geology. By now, the age of deposit formation is not