Magnetite lava flows in the Pleito-Melon District of the Chilean iron belt

(1982) concluded that this sequence was deposited in a volcanic island-arc setting. In the Pleito-Mel(n district the Bandurrias Group is composed principally ofandesitic lavas and volcanic breccias with intercalated rhyolitic tuffs and stratiform iron ores; the Bandurrias volcanics continues to the east of the area shown in Figure 2. An intrusive complex with tonalitic, granodioritic, and dioritic units crops out to the west and east of the volcanic sequence (Fig. 2). This complex has up to now been regarded as Tertiary in age (Moscoso et al., 1982), but our stratigraphic data indicate that parts of it may be Cretaceous and constitute a basement for the Bandurrias sequence. In the Berenguela area (Fig. 3) the diorite is younger than the Bandurrias andesites, which are recrystallized. A large number of rhyolitic dikes and a few andesitic ones cut extrusive as well as intrusive rocks, and some of the dikes may be feeders of the extrusions. Structures There are three fault systems in the district, all of them part of the Atacama megafault (cf. Thiele and Pincheira, 1987). The most important systems follow north-northeast and northwest to north-northwest directions and the third one consists of secondary east to east-northeast faults. The north-northeast system is longitudinal and seems to be the oldest. It has produced downfaulted blocks, for example in the E1 Mel(n area (Fig. 3), and many of the iron ores in the district are associated with it. The north