Abstract

The La Zarza orebody, containing some 100,000,000 metric tons of ore, is one of the three most important ones in the Huelva Province, Spain. It overlies the second phase of acid volcanic activity within a volcanic-sedimentary succession of Visean age.The stratigraphically lower part of the orebody consists of a finely bedded polymetallic ore, overlain by a massive pyrite facies (90% of the orebody), which is in turn covered by a more or less discontinuous, resedimented pyritic capping. The distribution of the metals within the orebody differs from the classical pattern. In La Zarza the Pb-Zn contents are greater in the lower parts of the deposit than in the upper parts, while Cu is more or less independent of other metals and shows a typical basal concentration in a breccia-type ore and stockwork restricted to a small area.The foot- and hanging walls are made up of acid epiclastic rocks and pelites and are practically without lavas; however, it is possible to recognize volcanic eruption centers some kilometers to the east of the mine. Below the sulfide orebody an intensively chloritized zone some hundred meters in diameter most probably represents a hydrothermally altered pipe.Overall, the wall rocks are characterized by their enrichment in Mg and impoverishment in Na and Si. Within the chloritized pipe, an overall lowering of alkali values is accompanied by a strong increase in Mg. As analyzed by spectrometry and atomic absorption, the distribution of trace elements in wall rocks and ore (Cu, Pb, Zn, V, Co, Cr, and Mn) tends to show the lack of consanguinity between ore and wall rocks on the one hand and the reasonably clear association between the ore and a late volcanic hydrothermalism on the other. Furthermore, the high Co/Ni ratios correspond to a hot sulfide deposition. There is no distinct dispersion halo, except for the presence of some disseminated sulfides around, and very close to, the ore. The distribution of the elements and their correlations differ betweeen the ore and wall rocks.Although it lies on a volcanic-sedimentary footwall, the La Zarza orebody is thus rooted in a hydrothermally altered pipe. Nevertheless the migration of magnesium and other metals is unconnected, and there is evidence of a certain independence among the different metals, above all in the case of copper.

First Page Preview

First page PDF preview
You do not currently have access to this article.