(They are the equivalent of the huts dotted over the map at the start of a Civ game.)
A distinctive icon is superimposed over the tile's terrain. A colony can work an LCR tile as normal, and natives can pass through them with no apparent change, but when a European unit enters the tile something definite happens (sometimes involving a dialogue with a choice) and the icon disappears for ever.
The worst possible outcome is the disappearance of the investigating unit. Positive results (guaranteed only after Hernando de Soto joins your congress, and possibly best achieved with scouts, and in the original game the term "positive" can include a zero result "You find nothing but rumors") go all the way up to the Fountain of Youth (giving you eight or more free emigrants) or a treasure worth thousands of gold pieces but needing a galleon to ship to Europe for redemption, which is taxable.
One of the best results is the Fountain of Youth, which puts eight new immigrants on the docks in Europe at no cost.
You discover a treasure train, usually worth three to five thousand gold pieces. It can move in the same turn. It can be captured by another European power or by natives (disappearing in the latter case). It needs to reach the seacoast, where one of your galleons can pick it up for transport to Europe, or to one of your ports, where you will get an offer from the King to transport it in one of his galleons very conveniently located for the purpose. He will take a large slice of the proceeds, but you get paid immediately and if you have no nearby galleons and/or you are at risk from marauding natives or other Europeans this may be the wise option.
You meet a starving survivor of a previous expedition, who becomes a loyal free colonist of yours at no actual cost although the text tells you he was given food and supplies. He can move in the same turn.
You may get the message "Our Scouts have improved to Seasoned status, Your Excellency!" (in the original game, with similar messages in FreeCol). Excellent result if your scout was a criminal and good if it was a servant. In the original game the scout who had another speciality loses it. In FreeCol he appears to retain the dual status.
You may be invited to sit by the fire and learn about nearby lands. Generally you see the map of every land tile within six in any direction. Early in the game, that can be very useful in telling you where scouts or ships should go or not go. Later it can be quite useless when you have already seen all the land.
Minor discoveries are usually a few trinkets worth between 50 and 117 gold in FreeCol and similar in the original.