fill the crater of Alumbrera, which has alum, ochre and sulfur colours. La Laguna is smaller than Alumbrera: The cone is only high and wide, with a deep crater. As with Alumbrera La Laguna features one fissure vent and a lava flow field, with a smaller volume of and surface area of . Both La Laguna and Alumbrera were fed by northwest-striking fissures, which is unusual as most lineaments in the area strike northeastwards or north–south. The surfaces of erupted rocks have been subject to various degrees of wind-driven erosion which has left grooves in the most altered units. Most likely the magma supply at these two vents was so large that the rising dykes were able to force pre-existent lineaments open and to pass through them. Composition Alumbrera and La Laguna has erupted alkaline to sub-alkaline basaltic trachyandesite to trachybasalt with a porphyritic texture. Phenocrysts within the rock include olivine and plagioclase or clinopyroxene, which form also the bulk of the matrix. The Jote lavas have similar composition to the La Laguna rocks. The chemical composition of the old and the new La Laguna volcanoes is different, with the old lavas showing a more volcanic arc-like composition. "Alum" (in reality a mixture of aluminium sulfate and magnesium sulfate) found at Alumbrera was mined by the local population. Eruptive history Eruptions at Alumbrera occurred in two phases, the first formed toothpaste lava and aa lava and the second in addition to lava small pyroclastic flows and a tephra blanket. A scoria fallout is found as far as east of Alumbrera. During this second phase, the sector collapse at Alumbrera occurred and was followed by the emission of lava bombs during Strombolian eruptions. La Laguna at first erupted several now heavily eroded lava flows and formed an old cone. Later during a second phase of activity lava bombs and scoria formed a newer cone and two lava flow fields. At both volcanoes, phreatomagmatic activity may have occurred after the magma pressure dropped so far that water could enter the conduit. The eruptions probably lasted several weeks to several years. A lava flow at La Laguna cone has been dated to 340,000 ± 60,000 years before present, consistent with its older appearance. A large-scale research project in the Puna yielded a number of Ar-Ar and K-Ar dates, including 3.2 and 4.5 million years ago for Jote and 0.3 and 7.3 million years