Situation and perspectives of the marbles of San Juan (Argentina)

Introduction

In the province of San Juan there are important deposits of marbles which have an intermittent production since many decades, in three well defined districts:

- District San Juan Centre (Pie de Palo-La Laja)
- District San Juan Sur (Divisadero / Cieneguita)
- District San Juan East (Valle Fértil)

Currently the only area where production is going on is the District San Juan South, about 85 km away to the southwest of the capital of the province (Fig.1).

This district is characterized by its calcareous sedimentary type marbles in which predominate tonalities that vary from clear gray, brown or grayish brown, sometimes reddish, to black. The main production, which shows a certain continuity, corresponds to the Moroccan variety, of grayish brown tones with white and black veins, while the lunel varieties (gray with white or black veins in "spider form") and black "galaxy" or "tulum" are exploited intermittently in spite of there being important reserves.

Less exploited due to the limited reserves known till now appear the so called "Rosa Francia", "Rojo Verona" and "San Mauricio", of colours that attract for their uncommon beauty.

Deposits

The extraction of marbles of the South District are concentrated mainly in a small valley known as Potrerillo, which is reached from the locality of Cieneguita.

There one can see benches of sub-vertical position concordant with limestone and regional dolomites. The black marble that appears in the extreme north of the valley, is a compact rock of fine grain of black colour with few veins of white colour of less than 1 mm (Fig.2).

It is present in banks of 1.5 to 3 metres thickness, compact, in an open front that oscillates between 20 and 40 metres wide.

The stone benches of Moroccan marble occupy the entire highland range covered by the valley to the west. This includes a compact rock of fine coloured grain, predominantly clear gray intermixed with white colour veins of less than 30 mm, with simple metal clipping fissures of less than 1 mm full of ferrous oxide (fig. 3). The uncovered stone benches have thickness of between 0.50 to 2 metres, even though the rudimentary methods applied up to now make it difficult to appreciate the exact value.

Regarding the manifestations of reddish marbles known as "Rosa Francia", "Rojo Venato" and "San Mauricio", its deposits consist of fault openings re-cemented and coloured by ferrous oxide of diverse intensity. The structures incline between 70 and 90, with thickness varying between 0,5 and 2,50 m (Fig. 4).

Physical-Mechanical characteristics

Physical-mechanical tests corresponding to European norms were conducted, the results of which are summarized in the table below (Fig. 5):

Exploitation

The extraction of the marbles was done by means of open air quarry fronts, making use of the sub-vertical position of the benches. The work done in black marble are located in the extreme north of the valley, taking the benches according to its direction.
In the case of Moroccan exist two sectors well differentiated:

A. A hillock that comes up inside the valley, exploited from north to the south.

B. Several new fronts in the western lower slope, in small quarries, which make use of benches with potentially important reserves.

In the case of reddish marbles, the work done in open air to date is small, destined in particular for producing small sized stone pieces.