Silver Ore is a fairly-common type of Terrain Special - specifically one of the Minerals. This mineral appears as a group of silvery specks on the overland map, and is found only on Hill and Mountain tiles by default. Silver Ore appears to be equally common on Myrror as it is on Arcanus.
The presence of a single tile of Silver Ore within the catchment area of a Town will raise that town's Gold output by exactly 
+2. This can be further boosted by the presence of the Marketplace, Bank, and/or Miners' Guild in this town.
Silver Ore can be changed into Mithril Ore using the Transmute spell, and Mithril Ore can be changed into Silver Ore using the same method. Silver Ore can be removed from a tile by raising a Volcano in that tile. Corruption temporarily removes the bonus that Silver Ore gives to nearby towns.
Description[]
Of all "precious" metals, silver is by far the most abundant. This shiny metal is too soft to be used in warfare, but is pretty enough to make it a good choice for fancy cutlery and jewelry. It is also significantly more common than gold, lowering its value enough to make it widely available. As a result, silver is also a good choice for low-denomination currency.
In the game, Silver Ore is represented by a group of white-colored (silvery) specks. Due to its color, it is often hard to spot on top of Mountain tiles, which are also mostly white. It is also somewhat hard to distinguish between Silver Ore and Mithril Ore tiles, which look very much alike. When it doubt, use the surveyor tool.
Initial Placement and Terrain[]
Silver Ore is one of the more common Terrain Specials. It appears at about the same frequency as Iron Ore or Coal, and is quite abundant on both Arcanus and Myrror.
Silver Ore appears only on Hills and Mountains. Since the process of placing Minerals on the game world is randomal in nature, it is possible that no Silver Ore will occur on either or both Planes, but this is a very rare occurrence.
The only way to remove Silver Ore is to raise a new Volcano underneath it. This permanently removes Silver Ore from the affected tile - and it cannot be restored. Volcanoes can be created using either the Raise Volcano or Armageddon spells.
Mineral Effects[]
Silver Ore is a Mineral, and thus provides a bonus to nearby towns. This bonus is equal to exactly +2, but can be altered by various Town Buildings, if present.
Gold Bonus[]
The presence of a Silver Ore tile within the catchment area of a town increases the town's Gold output by exactly +2. In other words, the town will now produce 2 Gold every turn on top of what is produced from the town's citizens and other sources.
Note that this Gold bonus is not subjected to the current Tax Rate. The Silver Ore tile will yield exactly 2 even if the town has only one citizen who is a Farmer and the Tax Rate is set to 0.
However, as explained below, several Town Buildings can capitalize on the availability of Silver Ore to increase trade and make more money off it.
Town Building Bonuses[]
There are two types of Town Buildings which can affect the Gold output of the Silver Ore mineral.
First, the Miners' Guild building increases the base gold production of Silver Ore by 50%, to 3. Secondly, any Gold bonuses, including the Marketplace, Bank, Merchants' Guild, as well as Road/River/Ocean Gold and Prosperity, will also multiply the bonuses from Gems. A patch of Silver Ore near a city with all of those effects and a population of 25 would produce 14.
[]
It is possible to build two towns close enough together that their catchment areas overlap. Shared tiles are marked by a red "1/2" label, seen in each town's details screen.
When a Silver Ore mineral occupies a shared tile, it will give half of its benefit to each town. Therefore, each of these towns will only get +1 from the shared Silver Ore tile (instead of +2.
Note that it is quite possible for this state to change during play, as new towns are established and existing towns are destroyed. The Silver Ore tile's bonuses will be redistributed automatically in such events.
Transmutation[]
Using the Transmute spell from the 
Nature realm, it is possible to turn a Silver Ore mineral into Mithril Ore.
Mithril Ore is often seen as much more beneficial than Silver Ore. Not only does it produce 
Power instead of Gold, but it also allows a nearby town to produce 
Mithril Weapons for new units - assuming the Alchemists' Guild is available.
Remember that transmutation is not permanent: you can always cast the spell a second time to change Mithril Ore back into Silver Ore.
Corruption[]
The Corruption spell can be cast on a tile containing Silver Ore. In such an event, both the Silver Ore itself as well as the tile it is on will cease providing any bonuses to nearby towns.
To combat this, send Shamans or Priests to Purify the affected tile immediately. If several tiles are Corrupted, Silver Ore tiles usually have a low priority for Purification. Several spells, including Gaia's Blessing and Consecration, may also help if they are available.