Can I create a Tile game like Catan without coyright issues?

A couple of years ago we got bored playing all the Catan games and using the pieces we created our own game. It took us six months of trying new things but we've now been playing our version for about a year and a half. We have introduced it to about 50 Catan players, all of them loved our version, in fact most say they want our version over all the others of Catan. We've played it hundreds of times and have taken it to several game parties where it is the hit of the party.

We use all the Catan pieces; resource tiles (grain, wood, brick, stone, sheep, gold, jungle water with prots water without ports) resource cards, roling for resources, cities, settlements roads, ships, and the robber (but to us it plagues just a single city) and the general idea of Catan. So some of the play is similar to Catan.

However, we play with all 67 pieces upside down to start the game and can only be turned over as they are discovered. We have added a single 10 sided die, there are 30 "treasure" that you can buy when you uncover empty water, you can purchase other things such as city walls and scouts too. There are more things to do and the resources are evenly distributed in the purchasing of "stuff" unlike Catan. And a lot fo the game play is impacted by the treasures in the ocean. The idea is to discover as much of the baord as you can and get to 15 points before everyone else to win.

I want to create the game, publish it and sell it, but I don't know what the copyright is for Catan. Can I create a game that is similar, but different? Do I need to make all new resources? Do I need to change other things to be able to do it?

I know that others have created knock-offs of catan and sold them. I just need someone to tell me what I can andcannot do.