1) Immobile element analysis was used to identify volcanic rock types at the Kristineberg VMS deposit in Sweden, despite extensive alteration and metamorphism. This helped correlate units between drill holes. 2) A chemostratigraphic sequence was determined, with rhyolite A south of lens B and rhyolite X north of lens A, separated by andesitic to rhyodacitic rocks hosting the lenses. 3) Calculated alterations show strong asymmetric envelopes up to 50m from lenses, with additions of Mg, Fe, and Si losses.

3. Kristineberg VMS deposit, western Skellefte belt The Kristineberg area in the western Skellefte district of northern Sweden is underlain by a thick sequence of early Proterozoic felsic and lesser mafic metavolcanic rocks of the Skellefte group, and overlying fine-grained turbiditic metasediments of the Vargfors group, all of which are deformed into large-scale folds that plunge to the west (Edelman, 1967; Grip, 1978) (Fig. 1). The Kristineberg deposit, which has produced 21.8 Mt grading 1.18 g/t Au, 36 g/t Ag, 1.0 % Cu, 3.65 % Zn, 0.24 % Pb, 26.0 % S, lies within altered and metamorphosed volcanic rocks containing muscovite, quartz, chlorite, talc, phlogopite, biotite, cordierite, andalusite, pyrite and magnetite. Schistose textures are common, while primary textures are rare. The ores lies within a few 100 metres of the Viterliden Intrusive Complex, dated at 1907±13 Ma (Bergström et al., 1999). Figure 1. General geology of the Kristineberg area. Locations of sections 1900 and 2500 east are shown.

4. Kristineberg -- general geology The Kristineberg deposit consists of two main massive sulfide horizons, the A- and B-ores, separated by 100-150 m, and the Einarsson Zone, a complex interval of Cu-Au-rich ‘stockwork’ sulfides in deformed rocks near the 1000 m level. In many areas, precursor rock types are almost impossible to identify due to abundant alteration and metamorphic minerals. To the south of the B-ores, massive rhyolite eventually appears, while to the north is the mine porphyry which represents a marginal phase of the Viterliden intrusion. One of the objectives of this study was to determine the precursors of the host rocks of the main ore lenses. Figure 2. General geology of the Kristineberg deposit on section 1900, showing the two main massive sulfide lenses (A- and B-ores) and the Einarsson Zone (E-zone).

5. Kristineberg -- use of immobile elements to identify rock types A. Application of immobile-element methods to 250 recent and 150 new lithogeochemical analyses has allowed several rock types to be chemically identified and correlated on the sections. Rhyolite A lies south of the B-ore horizon, while rhyolite X lies north of the A-ore horizon. Between these horizons are 100-200 m of cordierite-bearing schists ranging from andesite to rhyolite B. B. Immobile-element plots for rhyolite A and best-fit alteration lines. Least-altered rhyolite A is shown by the open circle in each plot. The Zr/Y plot together with REE data indicate that rhyolite A is of calc-alkaline affinity.

6. Kristineberg -- logging vs chemically defined units Rocks which previously could only be classified on the basis of their dominant mineral assemblage as various types of schist (left column) have been separated using their immobile-element signatures (right column) into the following chemical groups: rhyolite A, rhyolite B, dacite, andesite, basalt and mine porphyry. Massive rhyolite A lies immediately south of the B-ore horizon and Einarsson Zone, and is interpreted to form much of the stratigraphic footwall. A thick interval of mainly andesitic to dacitic to rhyolite B rocks, displaying remnants of volcaniclastic textures, makes up the interval between the A- and B-ore horizons. Rhyolite X lies immediately north of the A-ore horizon.

7. Kristineberg -- primary chemostratigraphy Because a given primary rock type such as rhyolite A can display a wide range of alteration and metamorphic overprints, the use of immobile-element ratios greatly improves the identification and correlation of rock units. Downhole (50 m interval)

8. Kristineberg -- primary chemostratigraphy The immobile-element results indicate that rhyolite A lies immediately south of the B-ore lens and Einarsson Zone. It is interpreted to form much of the stratigraphic footwall. A series of originally andesitic to rhyodacitic rocks, now altered and metamorphosed, makes up the interval between the A- and B-ore horizons. Rhyolite X lies immediately north of the A-ore lens. Section 2500Y

9. Kristineberg -- primary chemostratigraphy Section 1900Y The chemically defined rock units show very similar relations on section 1900Y, 600 metres to the west of section 2500Y.

10. Kristineberg -- alteration Variable alteration of the same parental rock, followed by metamorphism, can produce very different assemblages, e.g. andalusite-quartz-muscovite and cordierite-chlorite-talc. On the other hand, these assemblages can also be formed from different parent rocks, e.g. rhyolite or andesite. Calculated mass changes, which are tied to immobile-element ratios, take into account the different parent rocks. Mass changes calculated for all rock types outline strong and asymmetrical alteration effects flanking the massive sulfide lenses, ranging from major mass gains (Si, Fe and Mg) to major mass losses (Si and alkalis). This example shows SiO2 mass changes in absolute weight % on section 2500 E. The cordierite-bearing interval between ore lenses A and B is less altered, with modest Mg gains and Si losses.

11. Alteration and metamorphic assemblages Secondary minerals at Kristineberg e.g. chlorite, cordierite, phlogopite, biotite, and talc, are mainly Mg-rich. Although cordierite can be produced by metamorphic reactions involving sericite and chlorite, these reactions usually produce either anthophyllite, which is absent, or a significant amount of phlogopite in addition to andalusite, which is not generally observed. It is proposed instead that the cordierite formed mainly by reaction of kaolinite and chlorite: Chlorite + Kaolinite + Quartz yields Cordierite + Water When chlorite is in excess of kaolinite, the assemblage Chl + Crd + Qz is formed. Where kaolinite is in excess of chlorite, the excess is converted to andalusite in the reaction: Kaolinite yields Andalusite + Quartz + Water In this case, the assemblage formed is Crd + And + Qz; all of the original chlorite is consumed in the reaction that produces cordierite. The common presence of cordierite + andalusite but without anthophyllite is proposed to have formed from an original low-pH alteration phase such as kaolinite, which reacted with chlorite during metamorphism to form cordierite, and, where present in excess, to also produce andalusite. Mineral compositions determined by EMP, by W.H. MacLean, McGill University.

12. Conclusions 1) Immobile-element methods have proved very useful in identifying the host rocks of the Kristineberg deposit, and in correlating units between drill holes. Even assemblages as contrasting as andalusite-quartz-muscovite and chlorite-cordierite-talc can be shown to have been derived from the same parental volcanic unit. 2) A general chemostratographic sequence has been constructed for the deposit, with rhyolite A on the southern side of the B sulfide horizon, and rhyolite X on the northern side of the A sulfide horizon. A complex package of mainly andesitic to rhyodacitic rocks lies between these two sulfide horizons. The sulfide lenses probably formed at two separate stratigraphic horizons, although some structural repetition cannot be ruled out. 3) Calculated mass changes outline envelopes of strong but asymmetrical alteration extending up to 50 m from the sulfide lenses, with large additions of Mg and locally Fe, and large additions or losses of silica. 4) We suggest that a VMS alteration assemblage of chlorite-sericite-kaolinite-quartz formed at the time of deposition of the massive sulfide lenses, under low pH conditions at the sericite-kaolinite reaction boundary. During metamorphism, the kaolinite reacted with chlorite to form cordierite, and excess kaolinite produced andalusite. 5) We suggest that massive rhyolite A formed a shallow footwall intrusion that may also have promoted hydrothermal activity in the area of the Einarsson zone.