Quebrada del Arroyo Sauce Mayo, Sierra de La Ramada, La Ramada y La Cruz, Burruyacú Department, Tucumán Province, Argentinai

Regional Level Types
Quebrada del Arroyo Sauce Mayo	Valley
Sierra de La Ramada	Sierra
La Ramada y La Cruz	Municipality
Burruyacú Department	Department
Tucumán Province	Province
Argentina	Country

Elevation: 690 m. above sea level.

Geological history, Mesozoic, Pirgua Formation:
Pirgua formation outcrops surround completely to the crystalline core of the Sierra de La Ramada and partially, in the northern half of the Sierra del Campo. The thickness of the same varies significantly from one place to another: 250 meters thick which is the maximum of the area was recorded in the "Quebrada de Rosayaco" (East of the field saw faldeo), southward this decreases rapidly, in the "Río Ranchos", for example, only reaches 30 meters. Further South disappears altogether to look again at the Sierra de La Ramada. At the southern end of this last saw in the "Quebrada de Sauce Mayo", senses the presence of basalts carriers of Olivine amygdaloid character. Despite the thick forest that largely prevent the comments, seems they are robes interspersed in the gap of the Pirgua Formation base. It also sees the basalts in direct contact on the formation Medina. This observation is repeated again more to the North and is possible to include these within the Pirgua formation basalts. Locally sees in this place the base gap presents important participation of material of volcanic origin; There is abundant shot altered basalt of violet colour that give all the gap this colour. Notice also whitish alterations, which are probably due to the kaolinization of the feldspars.
In the Quebrada del Arroyo Sauce Mayo, in the spot known as "Loma Chata", on the South-eastern slope of the saw the Ramada, emerges a basaltic olivinic, whose Petrology, composition body geochemistry and relationship with other basaltic bodies linked to the depositional history Group Salta in the Argentine Northwest. You can access the area of mineralization from the city of San Miguel de Tucuman provincial No. 304 route up the city of La Ramada and thence towards the West by a private road that leads to the mouth of the stream above. Body, greyish brown to black, is located in the basal levels of the Pirgua subgroup and exhibits disjunction columnar on both banks of the Creek, forming deep cliffs from the foot of saw up to 50 m upstream from the confluence of the Alpasorcones and Sauce Mayo creeks. Presents a hipidiomorphic porphyritic texture and holocrystalline, with a paste microcrystalline composed of small individuals of augite and plagioclase, zeolites, where is inserso microphenocrystals of olivine as individually duos euhedral to subhedral, rusty or theterados zeolites and sheets of biotite and mineopaque General mostly euhedral, consequential frequency of the oxidation of the pyroxenes. Disglobal irregularly, zeolite and calcite in lesser proportion vesicles were observed. The plagioclase and clinopyroxene are presented in small proportion as microliths, resulting not possible to determine the composition of the feldspar. Studied basalts would be related to other outcrops in the province of Tucumán, in the towns of El Cadillal and Cumbres del Periquillo, as dated by the K/Ar method yielded ages of 128 to 97 million years for the complex high vulcanites of Las Salinas, the El Cadillal training, and 111 ± 5 million years to the bajump olivinic of Cumbres del Periquillo. Also would be equivalent to the volcanobasic training tas the high on the northern slope of the Sierra de La Ramada.
Recent studies carried out jointly with the National University of Salta, Anomalitaron they analyze the geochemistry of the basalts of Sauce Mayo, classifying them as alkali basalts and volcanism. These observations are consistent with the made for the basal exuberance of the Pirgua subgroup. Also well correspond to the vulcanites of the first effusive cycle of the Salta group. Regarding their origin, are considered movements responsible for the for snowing information systems of tensional fractures submeridional, why extruyeron queuedas basaltic related especially to the base of the Pirgua subgroup. Volcanism is would have developed in a marginal position along the edges of the dorsal Salta-Jujuy and arc Pampeano.

Primary mineralization:
Olivine - Augite - plagioclase – pyroxenes (clinopyroxene) - zeolites - Biotite - calcite.

Chemical analysis of the basalts from the Arroyo Sauce Mayo:
-Oxides % by weight:
SiO2: 24,85
Al2O3: 12,42
Fe2O3: 10,98
MnO: 0,16
MgO: 10,71
CaO: 11,85
Na2O: 4,13
K2O: 0,74
P2O5: 0,77
TiO2: 22,72
Total:93,64.

-Traces items in ppm :
Rb:12
Sr:1207
Zr:185
Y:26
Nb:68
U:n/a
Th:4
Co:65
Ni:168
Cr:220
V:249
Ba:714.

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References