The volcanogenic Woodlawn Cu‐Pb‐Zn sulphide mineralization occurs within a low‐grade metamorphosed sequence of Middle to Upper Silurian felsic volcanics and fine‐grained sedimentary rocks. Studies on a total of 234 rock samples from diamond drill holes have delineated zones of hydrothermally altered rocks extending more than ∼500 m laterally from the main ore lens, at least ∼100 m into the foot wall and up to ∼200 m into the hanging wall. These altered rocks contain virtually no remnants of primary feldspars and ferromagnesian minerals, and they are variably chloritized, sericitized and silicified. Chlorite and disseminated sulphide minerals are most abundant in zone I, a restricted zone of intense alteration immediately around the main ore lens, whereas sericitic muscovite is most abundant in the relatively extensive zone II, further from the ore. Silicification is also a feature of volcanics well beyond the limits of observed phyllosilicate‐rich alteration zones. Chemical changes within the hydrothermally altered rocks include major enrichment of Fe, Mg, S, Si and H2O, more sporadic enrichment of Ag, Ba, Bi, Cd, Cu, Mn, Pb, Sn and Zn, and major depletion of Ca, Na and Sr. K is depleted in zone I and shows considerable variation, but no overall depletion or enrichment, in zone II.