Preheat oven to 350 degrees Fahrenheit (177 degrees Celsius).
On 2 large baking sheets lined with parchment paper, lay out all of the nuts and seeds (except the hemp seeds) in a single flat layer. Bake for 12 minutes until just starting to turn golden.
Pour all of the toasted nuts and seeds into a large, heat-safe bowl. Add the hemp seeds and mulberries or goji berries. Mix well and set aside. Leave one sheet of parchment paper on one of the baking sheets and reserve the second parchment paper on the side. Set both aside.
In a small sauce-pot, combine the maple syrup, date syrup, and salt, and bring to a boil over medium high heat. Stir occasionally for 5 minutes. Working quickly but carefully, remove the mixture from the heat and immediately pour over the nuts and use a rubber spatula to quickly mix and then lay out flat on the parchment-lined baking sheet.
Use the second parchment sheet to push down the mixture into about 1 inch (2.5cm) high single flat rectangular shaped layer. Remove the top sheet and let the nut mixture cool and harden for 30 minutes.
Once the nut mixture is hardened, cut it into rectangles. Melt the dark chocolate in a double boiler, and then using a spoon or pastry bag, drizzle the chocolate over the bars and allow to harden, about 15 minutes.
If desired, before you drizzle the chocolate over the top, you can dip the bottom of each nut bar in chocolate, to make a chocolate bottom, about ¼ inch (6mm) thick. Return each bar to the parchment paper, and them drizzle the remaining chocolate over the top.