Resource Distribution in Homebrewed Location

[Leicontis]

So, I'm running a campaign in the not-too-distant future that will be set on an unexplored island, where the PCs are part of an exploration/colonization expedition. This island is extremely remote, making teleportation and similar magical means of transport impractical and leaving them with only a couple of shipments of supplies per year. Also, a large part of their income will depend upon finding and sending back things that their sponsors on the mainland can make money from. As such, they will have considerable incentive to look for natural resources on the island. The question is, how do I determine what kind of mineral and botanical resources are available, where the PCs can find them, how accessible and plentiful they are, etc.?

I've got a good idea of the island's climate and its geological history: Tropical temperatures, with areas ranging from jungle to desert in humidity - this gives me the ability to play with a variety of terrain types with which to challenge the PCs, and increases the likely biodiversity. Obviously, there will be a lot of interesting plants in the jungle area, and I'd like there to be at least one or two that can be used or refined into something useful and interesting (like a healing salve, antitoxin, or somesuch).

The island was originally two islands formed by uplift from the sea floor that collided due to tectonic movement, with a mountain range as the dividing line. This means a lot of limestone and/or marble, but I'm also having a bit of a subduction zone generate magma to turn one or more of the mountains into dormant volcanos, so igneous rock will be present as well. The latter suggests that there should be at least some veins of gold in the mountains, and a bit of gold available by panning from some rivers.

Lack of peat bogs also means coal is unlikely, but the ample timber available should offset that. Of course, the absence of the potential for coal would presumably make diamonds unlikely as well, wouldn't it?
Should I just pull resources out of a hat and drop them in random places on the map, or is there a more reasonable way to choose and place resource deposits? Obviously, the PCs could discover useful plants by watching how the wildlife interacts with them, but how besides finding them on the surface or just digging random holes (or later using a Rod of Metal and Mineral Detection or similar magic) could they discover mineral deposits?

I'm really new at this whole "building from scratch" thing, and would appreciate any advice those with some experience could give me!

[TheLogman]

Well, you seem to pretty much have it down as is.

Most volcanic islands have three parts to them.

1. The beach, surrounds the island, covered in sand. Few natural resources other than fish, pearls, and sea life.

2. The Jungle. Extends in a circle with a radius at the center to the beach. Contains rare animals, tropical trees and fruits, and other plant life. Remember that trees mostly spread via seeds, so trees never grow alone, but in groves. Birds are plentiful.

3. A mountain if applicable. Most commonly the center of the island, highest points on island. Diamonds are unlikely, as you said, because coal is probably not going to be plentiful. Other gemstones, however are possible, especially at lower levels of the island, in the mountain. If the Mountain occurred how you said it did, it's going to stretch deep below sea level, with caverns and such. Put some monsters, pirate treasure, whatever else in there.

Try to space out the resources, and maybe even guard them with monsters and the like if possible. An Assassin Vine will grow near fruit trees to eat things that go for the fruit. Monsters that eat stone or gemstones will live underground.

As for exact locations, other than being in the right biome, there's really no way to say exactly where any resource goes. Just try to space it out.

[Leicontis]

I'm also trying to place some more mundane resources like tin, copper, zinc, iron, etc. (and maybe mithral and/or adamantine) that the PCs could use to make useful items.

[kopout]

For monsters I would sugest things with Fly or Swim speeds. Or things that used to have them (flightless rok anyone).

[Leicontis]

For monsters I would sugest things with Fly or Swim soeads. Or things that used to have them (flightless rok anyone).
Ooh - me likey >:D

I've homebrewed a number of creatures and other hazards for the island, which I'll post on this board at some point. Some are just kinda weird, while others are just downright evil.

EDIT: Yeah, I was kinda hoping to save at least some of these for forum monster competitions. But, if already-posted monsters aren't allowed, pre-built but unposted monsters would be outside the spirit of the rules. Should I just post 'em and be done with it?

[sigurd]

I'm also trying to place some more mundane resources like tin, copper, zinc, iron, etc. (and maybe mithral and/or adamantine) that the PCs could use to make useful items.

Whats the time frame of the adventure. Typically, it will take way too long to bring your own raw goods from something like a mine into finished goods. You might be better to simply have a gold value for things (including mine deeds) and have the players buy\sell\or take a cut.

Sigurd

[Leicontis]

Whats the time frame of the adventure. Typically, it will take way too long to bring your own raw goods from something like a mine into finished goods. You might be better to simply have a gold value for things (including mine deeds) and have the players buy\sell\or take a cut.

Sigurd
This game is going to take place over months or years of in-game time, so there's a reasonable opportunity to refine raw goods. The fact that they'll only be able to send and receive goods with the mainland every few months at first also decreases the benefit they could get from shipping in refined and manufactured goods.