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As in many other districts of similar mineralization, the apparently stratiform sulfide orebodies of "Broken Hill type" at and around Broken Hill are almost invariably accompanied by thin beds of iron-rich sedimentary rock, loosely designated "banded iron formation." Representative occurrences of Broken Hill sulfide ore and iron formation have been systematically analyzed as whole rocks, and a preliminary account and comparison of their chemical constitutions is now given. The constitutional evidence supports earlier mineralogical work in indicating quite unequivocally that the two materials are consanguineous. Both show clear relationships between the incidence of "gangue" elements on one hand and of sulfides and oxides on the other. In both cases the major metals show a striking correlation with phosphate (as fluorapatite) and indeed the orebodies and banded iron formations both appear to be localized in phosphatic beds.Assuming, purely as a working hypothesis, that both rock types are of seafloor exhalative/hydrothermal origin (i.e., the result of volcanic or of artesian geothermal brine contributions to the contemporary seafloor), their el.emental constitutions are used to deduce possible sedimentary conditions under which the relevant precipitates were deposited. It is suggested that whether a particular exhalative episode led to the formation of sulfide ore or of banded iron formation depended on the rate and scale of emission of exhalative fluids and hence on the degree to which the latter modified the seafloor environment, and, in a qualitative way, on variation in composition of the exhalations related to differences in intensity of exhalative-hydrothermal activity from one episode to another.

Sulphur isotope measurements on five Australian stratiform lead-zinc sulphide ores are presented. Each deposit is characterised by a conspicuously narrow spread of values, mean g a~S heavier than meteoritic, average crustal, and, where sampled stratigraphically, 884S related to stratigraphy rather than propinquity. When considered with other deposits of the same class from elsewhere, several seemingly general features appear: Mean 8 a~S heavier than meteoritics; ranges for individual deposits narrow and rarely more than 8°/00 with standard deviation approximately l°/00 to 2O]0o; individual values for the whole group spread between, but almost entirely restricted by, the values for meteoritic S and seawater SO4"--; no age effect; no apparent relationship between ~ a4S and lead "type"; and, where investigated, a stratigraphical affiliation. While no positive interpretation of these features is made, it is suggested that the sulphur concerned has been derived neither from migrant hydro-thermal solutions nor from the H=S of normal biological sulphate reduction in seawater.Es werden MeBergebnisse "con fiinf australischen geschichteten Blei-Zink-SulfidLagerstiitten mitgeteilt: Jedes Vozkommen ist dutch einen bemerkenswert engen Schwankungsbereich der Werte, Mittelwert ~ ~S schwezer als meteoritischer Schwefel/Durchscbnittswert ans der Erdkruste, gekennzeichnet. Wo die Proben in stratigraphischer Abfolge entnommen wurden, zeigt der Weft 8 a~S eine stiirkefe Affinit/it zur Stratigraphie als zu absoluter Entfemung der Muster. Vergleicht man diese Werte mit solchen yon anderen Vorkommen der n/imlichen Lagerst/ittengruppe, so liegen einige allgemeine Eigenheiten auf der Hand: Fiir einige Vorkommen ist der Mittelwert g a4S schwerer Ms meteoritischer Schwefel; ftir einzelne Lagerst~tten ist der Bereich eng und iiberschreitet kaum mehr als 8°/00 mit der Standardabweichtmg yon ungef/ihr 1°/00 his 2°]oo; Einzelwerte ffir die gesamte Lagerstiittengruppe fallen fast ausschlieBlich zwischen die Werte fiir meteoritischen Schwefel und SO42--Ionan im Meerwasser; es herrscht kein dem geologischen Alter zuzuschreibender Effekt; such gibt es keine augenscheirdiche Beziehmag zwischen dem 8 a4S-Wert und dem Blei-,,Typ"; in jenen F~llen aber, wo Untersuchungsergebnisse vozliegen, ist eine Beziehung der Werte zur Stratigraphie zu erkennen. Obwohl keine positive Interpretation dieser Ph~-nomena angestelh wurde, wird die Vermutung ge~uBert, dab der betreffende sulfidische Schwefel weder yon wandernden hydrothen'nalen L6sungen noch yore H=S einer normalen biologischen Sulfatreduktion im Meerwasser abgeleitet werden karm.

This paper pursues the study of an apparent correlation between lead isotope abundance characteristics and features of the deposits in which the lead is discovered. New and precise analyses have been carried out on 55 galena samples, mostly From Australasian ore deposits classified as stratiform. To help clarify the interpretation, certain vein leads related to those which are stratiform have been included, as has one analysis of volcanic cotunnite.New evidence is offered that all leads began their isotopic evolution in a unique primary system which has very restricted spatial variation in the ratios U/Pb and Th/Pb. Leads from certain stratiform deposits approach more closely in isotopic composition the products of the primary system than do vein leads, many of which involve extensive crustal histories thai further modify the isotope ratios. The analyses presented here have sufficient precision to permit a close examination of the differences in isotope ratios between stratiform leads and the products of a simplified model for the primary system. The differences are significant and important.Novel aspects of the experimental technique are discussed.

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