Outcrop observations

The observations that should be reported are related to prospecting and not regular geological removal. Outcrop observation is the main stage of what is known as “Hammer prospecting”.

It is only in some desert or mountain regions that there are continues outcrops. In numerous regions, the outcrop is no more than a reduced area and a lot of time must be spent on its observation, following the bellow mentioned procedure:

• Break it in small pieces, preferably with a sledgehammer.
• Briefly determine the rock; remember that its easier to determine the structure of a rock when it’s wet
• In case of doubts on the determination of the rock, describe it and collect a sample of it no larger than a box of cigarettes in order to continue studying it for a precise determination (eventually asking coworker for advice) and keeping a thin part to study.
• The numbering of samples must be done carefully

NOTE: Each sample should be numbered with a permanent marker and put inside a plastic or cloth (preferred) bag, which should also be numbered.

If the sample is of loose material, write the number on a card, possibly of plastic and insert it inside bag.

For the numeration different methods can be adopted for example:

x) Each prospector is given initials and samples are numbered likewise, for example:

• Mauro Ficarelli MF 125
• Arthur Saks  AS 98
• Milton Andrews MA 25

xx) Defining a certain amount of samples for each team, for example:

team 1 Mauro Ficarelli from 0001 to 1000
team 2 Arthur Saks from 1001 to 2000
team 3 Milton Andrews from 2001 to 3000

The initials related to each sample will be put on the map and in the field book, along with their description, geographic coordinates or any other data that will make locating it easier (i.e. right side of the Mine river, location St. Marcus).

• Measure the direction and pitch stratification, of the slaty cleavage and significant fractures, along with alignments.
• Find simple view of mineralization and eventually with a magnifying glass, ask yourself if the rock has had any alteration, and find the oxidation materials. In tropical areas most outcrops are not found on the surface and in the best of cases they appear as a square meter of often unfertile attle, most made of metallic or oxidizing sulfuric mineral deposits which oxidation products are more or less soluble in stream water.   

Oxidized metals are stronger and among them there are magnetite, oligist oracular, chromo, and some other magnesium metals.

The existence of some of these minerals can be determined based on their color (see the notes on mineral deposits).

Special attention should be given to rocks that have been altered, with reddish, brown or black colors of oxide with Fe or Mn. If these formations are part of cavernous quartz more or less impregnated of ochre clay or haematite, it is very probable that they are the superficial part, the “tip of the iceberg” of a mineralized deposit. In depth examination will allow you to verify the existence of minerals or simply of its mold (boxworks).

Some petrographic modification of rocks can guide in the search because they are directly connected with useful minerals having formed at the same time by the same cause of modifications.

For example “tourmaline” or the impregnation of tourmaline substances, often appear close to tin deposits.

“Kaolinization” especially in acid erupted rocks (granite) the same as in trachyte & andesite, is accompanied by Sn and characterized in numerous case the presence of auriferous veins & auro-argentiferous.

“Dolomization” of calcareous rocks sometimes characterizes the presence of calamine, haematite and magnesium oxide in limestone.

“Propilitization”, is a kind of hydrothermal alteration that mainly affects magmatic volcanic rocks (andesine, etc) that turn green a cold with the development of sericite, chlorite, calcite, sulfurs and sometimes, mineralization with Au, Ag, Pb, Zn, Cu.

• In case of finding interesting mineralization, there has to be an indication of the percentage of the different useful minerals (see fig. 5) and specify how the mineralization is presented, the attle and main core: the veinlets that are followed by a joint or depending on the stratification, impregnations on the rock with useful material, with or without attle, stockwerk, possible presence of clay band, contact by faults of different natural terrain.